ANALYSIS OF THE TRANSITION FROM NORMAL MODES TO LOCAL MODES

Author Institution: Dipartimento di Chimica Fisica, Universit{\'a} di Palermo; Dipartimento di Fisica, Universit\'{a} di Milano; Laboratoire de Spectroscopic Moleculaire et Cristalline, Universtit{\'e} de Bordeaux 1By numerical integration of the classical equations of motion for a system of two coupled anharmonic oscillators, one can define the vibrational motions as follows: normal modes, for which energy is exchanged between the two oscillators and their phase difference is almost constant; local modes, for which the energy of one oscillator is always greater than the other’s and their phases are independent (1). We found a third type of modes, that we called transition modes, which show phase relation between the two oscillators and yet no energy exchange. They appear at total energy values intermediate between those typical for normal modes and for local modes. We tested our finding by two perturbative approaches, based on local modes and normal modes respectively. In this note we will point out the parameters favoring a wide extent of transition modes, in order to look for a spectroscopic signature of such modes. $^{1}$E. L. Sibert III, W. P. Reinhardt, J. T. Hynes, J. Chem. Phys., 77, 3583(1982