Quantum chemical estimation of the overtone contribution to the IR spectra of hydrocarbon halogen derivatives

The problem of a comparison of quantum chemical calculation results with the experimental characteristics of molecules is discussed, and it is noted that the accuracy of quantum computations can be most fully evaluated by a comparison of the theoretical results with the experimental spectra. By means of calculations, the contribution of anharmonism to the theoretical values of absorption band intensities in the IR spectra of 15 fluoro and 36 chloro derivatives of hydrocarbons is estimated. The first and second derivatives of the molecular dipole moment are obtained by ab initio quantum chemical calculations with the use of the 6–31G(1 d ) basis set and allowance for electron correlations by the second order Möller-Plesset method. The performed calculation well reproduces the positions of maxima and the intensity ratio of fundamental, overtone, and complex absorption bands.