Wavelength modulated absorption spectrum

Fig. 14. Preliminary infrared absorption spectra of the metal-molecule stretch mode for C Oand C Ointhec(4 x 2) structure on Pt(l 11) at 100 K recorded by a reflection wavelength modulation spectrometer. The recorded first derivative spectrum has been numerically integrated. Both spectra are reproduced in the figure.

Extended X-ray absorption fine structure (EXAFS) A technique for observing the local structure around a metal centre, using X-rays from a synchrotron source. The atom of interest absorbs photons at a characteristic wavelength and the emitted electrons, undergoing constructive or destructive interference as they are scattered by the surrounding atoms, modulate the absorption spectrum. The modulation frequency corresponds directly to the distance of the surrounding atoms while the amplitude is related to the type and number of atoms. In particular, bond lengths and coordination numbers may be derived. 

Synchroton radiation has been employed as a spectral source for a study of the absorption of HCN and DCN in the wavelength range 80—120nm. A vacuum-u.v. spectrophotometer for absorptions in the region 105—200 nm has been described. Solid-, liquid-, and gas-phase samples could be analysed at temperatures from —200 to 100 °C and at pressures between 0 and 150 atmospheres. The absorption spectrum of tra j-di-imide in the vacuum-u.v. has been measured. First-derivative u.v. spectroscopy has been employed in the analysis of Watts nickel plating solutions for trace amounts of saccharin. Impurity levels of 0.1 p.p.m. have been recorded. A wavelength modulated derivative spectrophotometer with a multi-pass absorption cell has been developed for the automatic analysis of atmospheric pollutants. Traces of SOj, NO, and NO2 were detected with limits of 15, 13, and Sp.p.b., respectively. A double-beam single-detector absorption spectrometer has been constructed. Independence... 

Fig. 1.61 Section of CS2-overtone spectrum. Comparison of optoacoustic detection (a) and absorption spectroscopy with wavelength modulation (b) (G.H. Wenz, Thesis, K.L.)...

Inoue et al. [43] has developed a derivative technique using a modified cassette recorder connected to a spectrophotometer. The same absorption spectrum was recorded on two separate parallel channels of a magnetic-tape cassette as frequency modulated (FM) analog signals with a slight shift in wavelength (--I nm). Then the difference between the output signals from these channels was recorded (Fig. 3-6). 

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