Accurate ab initio near-equilibrium potential energy and dipole moment functions of the X 2B1 and first excited A22 electronic states of OClO and OBrO

Abstract

Using highly correlated multireference configuration interaction wave functions with large correlation consistent basis sets, three-dimensional near-equilibrium potential energy functions (PEFs) have been calculated for the X 2B1 and first excited A22 electronic states of the atmospherically important OClO and OBrO radicals. The analytical PEFs have been used in perturbational and variational calculations of the anharmonic spectroscopic constants and vibrational spectra of both species. Excellent agreement with the available experimental data are observed for both species and electronic states, e.g., the vibrational fundamental frequencies in the ground electronic states are reproduced to within about 5 cm−1. For the A 2A2 state of OClO, it is demonstrated that the anomolously strong intensity of the ν3 mode in the UV absorption spectrum is due to strong anharmonic coupling between the stretching vibrations and not to a double minimum in the potential. Three-dimensional electric dipole moment functions have also been calculated for the ground electronic states of both species. These were used to calculate accurate absolute infrared absorption intensities for the fundamentals and low-lying overtones and combination bands of both species.