Hydrogen CARS spectrum

A typical IR spectrum, such as that of hexane in Eigure 13.31, appears as a series of absor-ption peaks of varying shape and intensity. Almost all organic compounds exhibit a peak or group of peaks near- 3000 cm due to car bon-hydrogen stretching. The peaks at 1460, 1380, and 725 cm are due to various bending vibrations. 

Not only the molecular ion peak but all the peaks in the mass spectrum of benzene are accompanied by a smaller peak one mass unit higher. Indeed, because all organic compounds contain car bon and most contain hydrogen, similar isotopic clusters will appear in the mass spectra of all organic compounds. 

The Raman spectrum of hydrogen sulfide H2S has been investigated at medium resolution in connection with the measurement of Raman scattering cross sections (Schrdtter and Kldckner, 1979). Later the g-branch of the v band was resolved using the cw CARS technique (Frunder et ah, 1985) and analysed by comparison with data from Fourier transform IR spectra (Lechuga-Fossat et ah, 1984). 

The reconstruction of the bandshape of the imidazole crystal was also performed using Car-Parrinello molecular dynamics (CPMD) simulation [73] of the unit cell of the crystal the results reproduce both the frequencies and intensities of the experimental IR spectrum of bands reasonably well, which we attribute to the application of dipole moment dynamics. The results are presented in Fig. 8 [70]. These and other recent CPMD calculations, on 2-hydroxy-5-nitrobenzamide crystal [71], oxalic acid dihydrate [72], and other systems [64-69], show that the CPMD method is adequate for spectroscopic investigations of complex systems with hydrogen bonds since it takes into account most of mechanisms determining the hydrogen bond dynamics (anharmonicity, couplings between vibrational modes, and intermolecular interactions in crystals). 

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