METHODS FOR CALCULATION OF ELECTRONIC VIBRATIONAL-SPECTRA OF POLYATOMIC-MOLECULES .1. OVERLAP INTEGRALS OF VIBRATIONAL WAVE-FUNCTIONS

A new, approximate method for computing the overlap integrals of vibra tional wave functions in the theory of polyatomic molecule vibronic sp ectra has been devised. The method is based on the quasi-orthogonality of the Dushinsky matrix as well as the reduction of the general probl em to consecutively allowing for the shift of normal coordinates and t heir mixing by excitation of the molecule. The calculation errors are less than 5% and the speed of operation is more than two orders greate r than that of the previous methods. So this method provides the possi bility of computing the vibrational structure of electronic spectra in the general case without invoking additional approximations (such as ignoring the Dushinsky effect). It will also be available for solving the inverse vibronic spectroscopy problems to determine the molecular structure in excited electronic states.