Effects of mode-mixing and non-Condon interaction in the vibronic spectra of multimode systems

A method of calculation of optical spectra, which allows one to take into account the mixing of an arbitrary number of modes in the transition, is developed. Thus the dependence of electronic transition matrix elements on nuclear coordinates is also taken into consideration. In this method, the calculation of the Fourier transform of the spectrum is reduced to the calculation of the determinant of the 2N×2N matrix and its reciprocal matrix; the elements of the matrix are given by time-dependent pair-correlation functions.