Ab initio infrared spectrum of lower frequency vibrations in cyclohexene: Paper I

Cyclohexene molecule possesses two low frequency modes assigned to the ring-twisting and ring-bending vibrations. In this paper, the ab initio potential energy associated with these vibrations is calculated at the MP2 level by varying a single internal variable (namely a dihedral angle of the molecule), by steps of two degrees. Calculation of the molecular dipole moment variation during the vibration and numerical integration of the equation of motion lead to infrared spectra in fairly good agreement with experimental ones. Potentials fitting the experimental spectra are presented and the comparison between calculated and fitted potentials is discussed.