Infrared Spectrometer Turnkey PCB Assembly

     Infrared spectrometer is an instrument that uses the absorption characteristics of substances to infrared radiation of different wavelengths to analyze molecular structure and chemical composition. An infrared spectrometer is usually composed of a light source, a monochromator, a detector and a computer processing information system. According to the different spectroscopic devices, it can be divided into dispersion type and interference type. For the dispersion-type dual optical path optical zero balance infrared spectrophotometer, when the sample absorbs a certain frequency of infrared radiation, the vibration energy level of the molecule transitions, and the light of the corresponding frequency in the transmitted beam is weakened, resulting in a reference The intensity difference between the light path and the corresponding radiation of the sample light path, so as to obtain the infrared spectrum of the measured sample.

1. Theory

    The infrared part of the electromagnetic spectrum can be divided into near-infrared light, mid-infrared light and far-infrared light according to its relationship with the visible spectrum. Far-infrared light (about 400-10 cm-1) is adjacent to microwaves and has low energy, which can be used for rotation spectroscopy. Mid-infrared light (approximately 4000-400 cm-1) can be used to study fundamental vibrations and associated rotation-vibration structures. Higher energy near-infrared light (14000-4000 cm-1) can excite overtones and harmonic vibrations. Infrared spectroscopy works on the basis that chemical bonds have different frequencies due to vibrational energy levels. The resonant or vibrational frequency depends on the shape of the molecular equipotential surfaces, the atomic mass, and ultimately the associated vibrational coupling. In order for a molecule's vibrational modes to become active in the infrared, there must be a permanent dipole change. Specifically, in the Born-Oppenheimer harmonic oscillator approximation, for example, when the molecular Hamiltonian energy corresponding to the electronic ground state is approximated by a harmonic oscillator near the equilibrium state of the molecular geometry, the potential surface of the molecular electronic energy ground state is determined by The natural oscillation mode of the , determines the resonant frequency. However, the resonant frequency is related to the strength of the bond and the atomic masses at both ends of the bond after an approximation. In this way, vibration frequencies can be associated with specific key patterns. Simple diatomic molecules have only one kind of bond, and that is stretching. More complex molecules may have many bonds, and vibrations may occur in conjugation, resulting in infrared absorption at certain characteristic frequencies that can be associated with chemical groups. The CH2 group, which is often found in organic compounds, can vibrate in six ways: "symmetrical and asymmetrical stretching", "scissor swinging", "left and right swinging", "up and down swinging" and "twisting".

2. Principle

     Schematic diagram of infrared spectrometer Fourier transform infrared spectrometer is called the third-generation infrared spectrometer. It uses Michelson interferometer to interfere with each other with two beams of polychromatic infrared light whose optical path difference changes at a certain speed, forming interference light, and then interacting with the sample. The detector sends the obtained interference signal to the computer for mathematical processing of Fourier transformation, and restores the interferogram into a spectrum.

3. Classification

     It is generally divided into two categories, one is raster scanning, which is rarely used; the other is Michelson interferometer scanning, called Fourier transform infrared spectroscopy, which is the most widely used. Grating scanning is to use a spectroscope to divide the detection light (infrared light) into two beams, one beam is used as a reference light, and the other beam is used as a probe light to irradiate the sample, and then the wavelength of the infrared light is separated by a grating and a monochromator, and scanned and detected one by one. The intensities of the wavelengths are finally integrated into a spectrum. Fourier transform infrared spectroscopy is to use Michelson interferometer to divide the detection light (infrared light) into two beams, which are reflected back to the beam splitter on the moving mirror and the fixed mirror. The two beams are broadband coherent light and will interfere. The coherent infrared light is irradiated on the sample, collected by the detector, and the infrared interferogram data containing the sample information is obtained. After the data is Fourier transformed by the computer, the infrared spectrum of the sample is obtained. Fourier transform infrared spectroscopy has the characteristics of fast scanning rate, high resolution, stable repeatability, etc., and is widely used.

4.Application field

    Perform compound identification Perform structural analysis of unknown compounds

    Carry out quantitative analysis of compounds to study the transient relationship between chemical reaction kinetics, crystal transition, phase transition, material tension and structure; continuous detection of industrial processes and air pollution; monitoring of free silica in the coal industry; health and quarantine , pharmacy, food, environmental protection, public security, petroleum, chemical industry, optical coating, optical communication, material science and many other fields. Jewelry industry detection, crystal quartz hydroxyl measurement, polymer composition analysis, drug analysis, etc.

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