Estimation of the contribution of absorption bands for overtones and composite frequencies in IR spectra of olefins and heteroatomic organic compounds

Intensities of fundamental, overtone, and composite absorption bands for 11 olefins, 17 nitrogen- and oxygen-containing organic compounds, and 12 sulfur-containing organic compounds are calculated in the anharmonic approximation. The first and second derivatives of the electric dipole moment of a molecule were calculated by the quantum-chemical ab initio MP2/6-31G(1d) approach. It is shown that, for the studied compounds, the average contribution of overtones and composite frequencies to absorption in the region from 100 to 4000 cm⁻¹ is of about 10%. The major contribution (on the average 80%) of overtones and composite frequencies falls in the regions (mainly from 1600 to 2800 cm⁻¹) where fundamental transitions are rarely observed. The calculations well describe the centers and intensities of the fundamental, overtone, and composite absorption bands and can be used for the standard-free spectrochemical determination of the compounds of interest by their overtone spectra.