A QUANTUM DYNAMICAL STUDY OF CH OVERTONES IN FLUOROFORM .1. A 9-DIMENSIONAL AB-INITIO SURFACE, VIBRATIONAL-SPECTRA AND DYNAMICS

In this series, the characteristics of intramolecular vibrational-ener gy redistribution (IVR) present in the CH overtones of CHF3 are invest igated. Particular attention is given to the multiple time scales and thus mechanisms present in the IVR dynamics. In Part I, a 9-dimensiona l ab initio potential energy surface is developed to adequately accoun t for the vibrational couplings of all modes. Furthermore, all-mode vi brational state calculations, of large-primitive space dimension, are performed using a recently developed wave operator sorting algorithm i n tandem with the recursive residue generation method. All fundamental s, first overtones, and bimodal combination states with up to 3 quanta are presented. Also, the A(1) and E-symmetry CH polyads are determine d through the second overtone. Equilibrium geometry, rotational consta nts, and vibrational properties agree quantitatively with experiment i n most cases. The error is systematic in origin and largely due to the error in the ab initio harmonic frequencies. New vibrational constant s and resonance interactions are reported for the background modes. In contrast to the prominent CH stretch-bend Fermi resonance structure, responsible for ultrafast (t<50 fs) energy transfer, the CH polyads al so exhibit vibrational fine structure of order I to 10 cm(-1) due to b ackground-mode coupling. This secondary coupling results in IVR on the picosecond time scale. (C) 1995 American Institute of Physics.