Simplified models for anharmonic numbers and densities of vibrational states. II. All the bound states of HO 2

Abstract

Anharmonic rovibrational densities of states play an important role in statistical unimolecular rate theory and suitable methods for their determination are in large demand. This article compares different approaches to their calculation using the bound states of HO 2 as an example. Nearly accurate results for this system are becoming available on the basis of ab initio calculations. After empirical correction of these results, the present work predicts a total number of bound vibrational states of 315 ± 5 (for the non-rotating molecule). Approximate methods at different levels of complexity can be validated against the results obtained. In particular, the empirical method from part I [J. Troe, Chem. Phys. 190 (1995) 381] is tested. Gaining confidence in the performance of the various methods is a necessary condition for further applications to larger molecules for which ab initio calculations are out of reach.