CLASSICAL DYNAMICS OF TWO COUPLED TORSIONAL MODES

Abstract

We have investigated numerically the classical dynamics of two HCOC torsions, sharing the C-O-C fragment. We have described completely their kinetic interaction through the formulae by Decius (1). We have assumed that their interconversion barriers are low, ranging around $200 cm^{-1}$, and we have also allowed for a potential interaction. We obtained similar results as previously found for two C-H stretchings, coupled with an effective harmonic interaction constant; at low total energy the system exhibits normal modes, at higher energy transition modes first and then local modes replace symmetric normal modes (2). The three types of modes have also been characterized via Fourier analysis. We found that the energy threshold for the appearance of local modes is twice the energy threshold for the appearance of transition modes. Some differences with respect to the case of C-H stretchings were found in the behaviour of local modes. Classical perturbation theory on the basis of normal modes allows to predict the qualitative features of the system, although it is not as good as in the case of reference (2) qualitatively.