AN ACCURATE AB-INITIO HOCL POTENTIAL-ENERGY SURFACE, VIBRATIONAL AND ROTATIONAL CALCULATIONS, AND COMPARISON WITH EXPERIMENT

Accurate ab initio multireference configuration interaction (CI) calcu lations with large correlation-consistent basis sets are performed for HOCl. After extrapolation to the complete basis set limit, the ab ini tio data are precisely fit to give a semiglobal three-dimensional pote ntial energy surface to describe HOCl-->Cl+OH from high overtone excit ation of the OH-stretch. The average absolute deviation between the ab initio and fitted energies is 4.2 cm(-1) for energies up to 60 kcal/m ol relative to the HOCl minimum. Vibrational energies of HOCl includin g the six overtones of the OH-stretch are computed using a vibrational -Cl method on the fitted potential and also on a slightly adjusted pot ential. Near-spectroscopic accuracy is obtained using the adjusted pot ential; the average absolute deviation between theory and experiment f or 19 experimentally reported states is 4.8 cm(-1). Very good agreemen t with experiment is also obtained for numerous rotational energies fo r the ground vibrational state, the ClO-stretch fundamental, and the f ifth overtone of the OH-stretch. (C) 1998 American Institute of Physic s.