Theoretical study of Hal3CH/F2CD2 (Hal = F, Cl) and F3CH/FH heterodimers with blue shifted hydrogen bonds

The geometric and spectroscopic features as well as an interaction energy of Hal3CH/F2CD2 (Hal = F, Cl) and F3CH/FH heterodimers have been studied using MP2(full)/6-31+G(d,p) ab initio calculations, with a priori BSSE correction method. The decomposition of the interaction energy into physically distinct contributions has been performed in the frame of the symmetry adapted perturbation theory (SAPT). The effect of the repulsion and attraction contributions on the change of the CH bond length and the frequency shift of the CH stretching normal vibration has been analysed, treating the interaction energy and anharmonic terms of the intramolecular potential energy of Hal3CH as a perturbation. In the case of strongly non-linear structures, the electrostatic contribution as well as the exchange component of the interaction energy, can contribute to a blue frequency shift of this vibration of fluoroform.