Ab initio treatment of the chemical reaction precursor complex Cl(P-2)-HF. 2 : Bound states and infrared spectrum

Abstract

Bound energy levels and properties of the Cl((2)p)-HF complex were obtained from full three-dimensional (3D) calculations, with the use of the ab initio computed diabatic potential surfaces from the preceding paper and the inclusion of spin-orbit coupling. For a better understanding of the dynamics of this complex we also computed a 21) model in which the HF bond length r was frozen at the vibrationally averaged values r(0) and r, and a 2 + ID model in which the 3D potentials were averaged over the nu(HF) = 0 and nu(HF) = 1 vibrational wave functions of free HE Also ID calculations were made in which both r and the Cl-HF distance R were frozen. The complex is found to have the linear hydrogen bonded Cl-HF structure, with ground-state quantum numbers J = (3)/(2) for the overall angular momentum and IQ I = 3/2 for its projection on the intermolecular axis R. The binding energy is Do = 432.25 cm(-1) for V-HF = 0 and D-0 = 497.21 cm(-1) for nu(HF) = 1. Bending modes with vertical bar Omega vertical bar = 1/2 and vertical bar Omega vertical bar = 5/2 are split by the Renner-Teller effect, since the electronic ground state is a degenerate (2)Pi state. A series of intermolecular (R) stretch modes was identified. Rotational constants and e-f parity splittings were extracted from the levels computed for J = 1/2 to 1/2. The computed red shift of the HF stretch frequency of 64.96 cm(-1) and the Cl-35-Cl-37 isotope shift of 0.033 cm(-1) are in good agreement with the values of 68.77 and 0.035 cm(-1) obtained from the recent experiment of Merritt et al. (Phys. Chem. Chem. Phys. 2005, 7, 67), after correction for the effect of the He nanodroplet matrix in which they were measured.