ANHARMONIC CORRECTIONS TO VIBRATIONAL TRANSITION INTENSITIES

The second-order pertubation theory formula for the dipole matrix element and integrated intensities of fundamental, first overtone, and combination transitions are presented. The formulas were derived by using contact transformation theory with the help of a computer algebra program, and checked numerically by comparing their results with intensities calculated by using normal Rayleigh-Schrödinger perturbation theory. The transformation of calculated dipole fields to molecule-fixed axes is also discussed. applications for H2O and H2CO are reported, using MP2 representations for the quartic force fields and cubic dipole fields. The anharmonic and Coriolis contributions to the integrated intensities are analyzed and the differences with experimental results discussed. © 1990 American Chemical Society.