The vibrational energy of the molecule is larger than the rotational energy. When the vibrational energy level transition occurs, it is inevitably accompanied by the transition of the rotational energy level, so the pure vibrational spectrum cannot be measured, but only the vibrational-rotational spectrum of the molecule can be obtained. This spectrum is called infrared absorption spectrum. Semiconductor wafers from PAM-XIAMEN can be tested by fourier transform infrared spectroscopy (FTIR) if necessary.
Infrared absorption spectrum is also a kind of molecular absorption spectrum. When the sample is irradiated by infrared light with continuously changing frequency, the molecule absorbs the radiation of certain frequencies and causes a net change in the dipole moment caused by its vibrational or rotational motion, resulting in the transition of the molecular vibrational and rotational energy levels from the ground state to the excited state, which weakens the transmitted light intensity corresponding to these absorption regions. The infrared spectrum is obtained by recording the relationship between the percent transmittance of infrared light and the wave number or wavelength.
The characteristics of fourier transform infrared spectroscopy (FTIR):
1) The scanning speed is fast, and the information of all frequencies can be measured simultaneously within the scanning time;
2) high resolution;
3) high sensitivity;
4) High precision.
1. Fourier Infrared Spectroscopy Instrument
Fourier infrared spectroscopy (FT-IR) instrument is composed of light source, Michelson interferometer, sample pool, detector and computer. The light emitted by the light source is converted into interference light through the interferometer. The interference light contains information of all wavelengths emitted by the light source. When the above interference light passes through the sample, the light of some wavelength is absorbed by the sample and becomes the interference light containing the sample information. The sample interferogram is collected by the computer, and the infrared spectrum of absorbance or transmittance changing with frequency or wavelength is obtained after the fast Fourier transform of the computer.
Fourier Infrared Spectrometer Structure
2. Applications of Infrared Spectroscopy
Infrared spectroscopy is widely used in the study of molecular structure and chemical composition of substances as “molecular fingerprints”. According to the position, intensity and shape of the band frequency obtained by the molecule after absorbing infrared light, and the relationship between the absorption band, temperature, aggregation state, etc., the spatial configuration of the molecule can be determined, and the force constant, bond length and bond angle of the chemical bond can be obtained. From the perspective of spectral analysis, the frequency of the characteristic absorption band is mainly used to infer the existence of a certain group or bond in the molecule, and the adjacent group or bond is inferred from the change of the frequency of the characteristic absorption band, and then the chemical structure of the molecule is determined. Mixtures and compounds can also be quantitatively analyzed by changes in the intensity of characteristic absorption bands.
Fourier transform infrared spectrometers are currently concentrated in the following areas:
1) Semiconductor materials
2) Pharmaceutical and chemical industry
3) Research of polymer materials
4) Petrochemical industry
6) Biomedical research
7) Forensic identification
8) Gas analysis
9) Atmospheric environment monitoring