Evaluation of vibrational partition functions for polyatomic systems:quantum versus classical methods for H_2O and Ar...CN

摘要

The vibrational partition function of H_2O and Ar... CN systems is calculated within the framework of quantum and classical statistical mechanics. The phase space integral arising in the classical picture is solved adopting an efficient Monte Carlo technique. The temperqature dependence of the partition function for the two molecules is exploited with a view to study the r ange of applicability of classical statisticla mechanics. For the case of Ar...CN van der Waals complex the role played by freezing the CN bond is also analyzed