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R Paschotta · 2 — A light beam is linearly polarized, which means that the electric field oscillates in a certain linear direction perpendicular to the beam axis.

(a) Distinguish between unpolarised light and linearly polarised light. How does one get linearly polarised light with the hel of a polaroid ? (b) A narrow beam of unpolarised light of intensity I0 is incident on a polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making angle of 60∘ relative to the pass axis of P1. find the intensity of the light transmitted by P2.

Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

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IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Mid infrared

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Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Infrared wavelength

Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

[4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Infraredlight

Fig-1 IR Spectrum [2] Infrared absorption spectroscopy Infrared absorption spectroscopy is the method to determine the structures of molecules with the molecule’s characteristic absorption of infrared radiation. The infrared spectrum is nothing but a molecular vibrational spectrum that when exposed to infrared radiation; sample molecules selectively absorb radiation of specific wavelengths causing a change in the dipole moment of sample molecules. Consequently, the vibrational energy levels of sample molecules are transferred from the ground state to the excited state. The frequency of the absorption peak in the molecules is determined by the vibrational energy gap. The number of absorption peaks is related to the number of vibrational freedoms of the molecule and the intensity of absorption peaks is related to the change of dipole moment corresponding to the possibility of the transition of energy levels [3]. Therefore, analyzing the infrared spectrum helps in obtaining the various structural information of a molecule. The different IR absorption spectrometer setups are shown in the Fig-2. Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

[3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

[2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Distinguish between unpolarised and plane polarised light. An unpolarised light is incident on the boundary between two transparent media. State the consition when the reflected wave is totally plane polarised. Find out the expression for the angle of incidence in this case.

[1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

(a) Distinguish between unpolarized light and linearly polarized light. How does one get linearly polarised light with the help of a plaroid ? (b) A narrow beam of unpolarised light of intensity I0 is incident on a polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making angle of 60∘ relative to the pass axis of P1. Find the intensity of the light transmitted by P2.

Image

Near-infrared wavelength

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(a) Distinguish between unpolarized light and linearly polarized light. How does one get linearly polarised light with the help of a plaroid ? (b) A narrow beam of unpolarised light of intensity I0 is incident on a polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making angle of 60∘ relative to the pass axis of P1. Find the intensity of the light transmitted by P2.

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Fig-1 IR Spectrum [2] Infrared absorption spectroscopy Infrared absorption spectroscopy is the method to determine the structures of molecules with the molecule’s characteristic absorption of infrared radiation. The infrared spectrum is nothing but a molecular vibrational spectrum that when exposed to infrared radiation; sample molecules selectively absorb radiation of specific wavelengths causing a change in the dipole moment of sample molecules. Consequently, the vibrational energy levels of sample molecules are transferred from the ground state to the excited state. The frequency of the absorption peak in the molecules is determined by the vibrational energy gap. The number of absorption peaks is related to the number of vibrational freedoms of the molecule and the intensity of absorption peaks is related to the change of dipole moment corresponding to the possibility of the transition of energy levels [3]. Therefore, analyzing the infrared spectrum helps in obtaining the various structural information of a molecule. The different IR absorption spectrometer setups are shown in the Fig-2. Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

infrared中文

Infrared Spectroscopy is a technique for analyzing the interaction of molecules with infrared light. The range of Infrared region is 12800 ~ 10 cm-1 and can be divided into near-infrared region (12800 ~ 4000 cm-1), mid-infrared region (4000 ~ 200 cm-1) and far-infrared region (50 ~ 1000 cm-1). The concept of IR spectroscopy can be generally analyzed in three different ways first one by measuring reflection, second by emission, and third by absorption. The major use of infrared spectroscopy is to determine the functional groups of molecules, relevant to both organic and inorganic chemistry An IR spectrum is essentially a graph plotted with the frequency or wavelength on the X-axis and infrared light absorbed on the Y-axis. An illustration highlighting the different regions that light can be classified into is shown in Fig-1. IR Spectroscopy detects frequencies of infrared light that are absorbed by a molecule and this absorption takes place due to the ability of molecular bonds that are corresponding to the specific frequency [1]. Fig-1 IR Spectrum [2] Infrared absorption spectroscopy Infrared absorption spectroscopy is the method to determine the structures of molecules with the molecule’s characteristic absorption of infrared radiation. The infrared spectrum is nothing but a molecular vibrational spectrum that when exposed to infrared radiation; sample molecules selectively absorb radiation of specific wavelengths causing a change in the dipole moment of sample molecules. Consequently, the vibrational energy levels of sample molecules are transferred from the ground state to the excited state. The frequency of the absorption peak in the molecules is determined by the vibrational energy gap. The number of absorption peaks is related to the number of vibrational freedoms of the molecule and the intensity of absorption peaks is related to the change of dipole moment corresponding to the possibility of the transition of energy levels [3]. Therefore, analyzing the infrared spectrum helps in obtaining the various structural information of a molecule. The different IR absorption spectrometer setups are shown in the Fig-2. Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Light spectrum

The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

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[5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Light waves are electromagnetic waves and hence transverse in nature. The electric field in a light wave propagating in free space is perpendicular to the direction of propagation. But there are infinite number of directions perpendicular to the direction of propagation. but there are infinite number of directions perpendicular to the direction of propagation of light. for example if light propagates along x-axis, the electric field may be along y-axis or along the z-axis or along any direction in y-z plane in the ordinary light. However, if electric field →E remains parallel to a fixed direction (say y-axis) then such light is called linearly polarised light. There are several methods to produce polarised light from the unpolarised light. now-a-days polaroid sheets are commonly used to produce linearly polarised light. a polaroid has long chain of hydrocarbons which become conducting at optical frequencies. when light falls normally on the polaroid sheet, the →E parallel to the chains is absorbed in setting up electric currents in the chains but →E perpendicular to the chain gets transmitted. so, light on passing through the polaroid i.e., the transmitted light become linearly polarised with →E parallel to the transission (pass) axis of polaroid. If linearly polarised light of intensity 'I' is incident on another polaroid whose pass axis is inclined at an angle θ from pass axis of first polaroid (or transmission axis of →E of linearly polarised light) the intensity of transmitted light It is given as: It=Icos2θ. Q. What is linearly polarised light ?

(a) Distinguish between unpolarized light and linearly polarized light. How does one get linearly polarised light with the help of a plaroid ? (b) A narrow beam of unpolarised light of intensity I0 is incident on a polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making angle of 60∘ relative to the pass axis of P1. Find the intensity of the light transmitted by P2.

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Distinguish between unpolarised and plane polarised light. An unpolarised light is incident on the boundary between two transparent media. State the condition when the reflected wave is totally plane polarised. Find out the expression for the angle of incidence in this case.

I am a postgraduate researcher at the University of Leeds. I have completed my master's degree in the Erasmus Tribos program at the University of Leeds, University of Ljubljana, and University of Coimbra and my bachelor's degree in Mechanical Engineering from VTU in NMIT, India. I am an editor and social networking manager at TriboNet. I have a YouTube channel called Tribo Geek where I upload videos on travel, research life, and topics for master's and PhD students.

Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

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Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

Infrared (IR) spectroscopy deals with the infrared region of the electromagnetic spectrum, i.e., light having a longer wavelength and a lower frequency than visible light. Infrared light was discovered in the 19th century which led to the use of infrared lights in various applications. Definition Infrared Spectroscopy is a technique for analyzing the interaction of molecules with infrared light. The range of Infrared region is 12800 ~ 10 cm-1 and can be divided into near-infrared region (12800 ~ 4000 cm-1), mid-infrared region (4000 ~ 200 cm-1) and far-infrared region (50 ~ 1000 cm-1). The concept of IR spectroscopy can be generally analyzed in three different ways first one by measuring reflection, second by emission, and third by absorption. The major use of infrared spectroscopy is to determine the functional groups of molecules, relevant to both organic and inorganic chemistry An IR spectrum is essentially a graph plotted with the frequency or wavelength on the X-axis and infrared light absorbed on the Y-axis. An illustration highlighting the different regions that light can be classified into is shown in Fig-1. IR Spectroscopy detects frequencies of infrared light that are absorbed by a molecule and this absorption takes place due to the ability of molecular bonds that are corresponding to the specific frequency [1]. Fig-1 IR Spectrum [2] Infrared absorption spectroscopy Infrared absorption spectroscopy is the method to determine the structures of molecules with the molecule’s characteristic absorption of infrared radiation. The infrared spectrum is nothing but a molecular vibrational spectrum that when exposed to infrared radiation; sample molecules selectively absorb radiation of specific wavelengths causing a change in the dipole moment of sample molecules. Consequently, the vibrational energy levels of sample molecules are transferred from the ground state to the excited state. The frequency of the absorption peak in the molecules is determined by the vibrational energy gap. The number of absorption peaks is related to the number of vibrational freedoms of the molecule and the intensity of absorption peaks is related to the change of dipole moment corresponding to the possibility of the transition of energy levels [3]. Therefore, analyzing the infrared spectrum helps in obtaining the various structural information of a molecule. The different IR absorption spectrometer setups are shown in the Fig-2. Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html

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Infrared absorption spectroscopy is the method to determine the structures of molecules with the molecule’s characteristic absorption of infrared radiation. The infrared spectrum is nothing but a molecular vibrational spectrum that when exposed to infrared radiation; sample molecules selectively absorb radiation of specific wavelengths causing a change in the dipole moment of sample molecules. Consequently, the vibrational energy levels of sample molecules are transferred from the ground state to the excited state. The frequency of the absorption peak in the molecules is determined by the vibrational energy gap. The number of absorption peaks is related to the number of vibrational freedoms of the molecule and the intensity of absorption peaks is related to the change of dipole moment corresponding to the possibility of the transition of energy levels [3]. Therefore, analyzing the infrared spectrum helps in obtaining the various structural information of a molecule. The different IR absorption spectrometer setups are shown in the Fig-2. Fig-2 Absorption IR spectrometer setups [4] Dispersive IR Spectrometers Dispersive IR Spectrometers are used to generate the spectra by dispersing the incoming radiations into frequency or spectral components. The common examples of dispersive elements are gratings and prisms that disperse the incoming spectrum of radiation. There are mainly two types of dispersive spectrometers; they are monochromators and spectrographs. The major difference between these two spectrometers is the case monochromators use a single detector, a narrow slit, and a rotating dispersive element that allows the user to observe the selected wavelengths. Whereas spectrographs use an array of detector elements and a stationary dispersive element which helps in obtaining a wide range of wavelengths at the same time. The schematic image of the monochromator dispersive spectrometer is shown in the Fig-3. Fig-3 Schematic image of the monochromator dispersive spectrometer [5] Components of IR spectrometers The basic components of an IR spectrometer include a radiation source, monochromator, and detector. The schematic representation of the IR spectrometer with its components is shown in Fig-4. IR radiation source: The commonly used IR radiation sources are inert solids that are heated electrically to promote the thermal emission of radiation in the infrared region of the electromagnetic spectrum. Monochromator: The monochromator is a device that is used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies. After the incident radiation travels through the sample species, the emitted wavefront of radiation is dispersed by a monochromator (gratings and slits) into its component frequencies. A combination of prisms or gratings with variable-slit mechanisms, mirrors, and filters comprise the dispersive system. Narrower slits give better resolution by distinguishing more closely spaced frequencies of radiation and wider slits allow more light to reach the detector and provide better system sensitivity. The emitted wavefront beam (analog spectral output) hits the detector and generates an electrical signal as a response. Detectors: Detectors are devices that are used to convert the analog spectral output into an electrical signal. These electrical signals are further processed by the computer using a mathematical algorithm into a final spectrum. The detectors that are used in IR spectrometers can be classified as either photon/quantum detectors or thermal detectors. It is the absorption of IR radiation by the sample, producing a change in IR radiation intensity, which gets detected as an off-null signal (e.g. different from the reference signal). This change is translated into the recorder response through the actions of synchronous motors. Each frequency that passes through the sample is measured individually by the detector which consequently slows the process of scanning the entire IR region. Fig-4 Dispersive IR spectrometer [6] Reference: [1] Nancy Birkner (UCD), and Qian Wang (UCD) on chem.libretexts.org [2]https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ [3] B. C. Smith, Fundamentals of Fourier Transform Infrared Spectroscopy, CRC press, 1996 [4] Zaera, F., 2014. New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions. Chemical Society Reviews, 43(22), pp.7624-7663. [5] https://spie.org/publications/tt61_121_dispersive_spectrometers?SSO=1 [6] https://www.chemicool.com/definition/fourier_transform_infrared_spectrometer_ftir.html