CALCULATION OF VIBRATIONAL LINE SHIFTS FOR MOLECULAR DIMERS

A method for calculating the shifts of vibrational excitation frequencies in molecular clusters is presented. It is based on second order non-degenerate perturbation theory and refers to early publications of Buckingham. The resulting formula involves off-diagonal cubic force constants thus accounting for coupling of the individual molecular normal modes. It is applied to the CO stretching mode in methanol dimers and to all three modes in water dimers. The results are in good agreement with experimental values with exception of the ν3-mode of the donor molecule in the water dimer where the perturbation approach was found to be not adequate. © 1990.