Adiabatic-hindered-rotor treatment of the parahydrogen-water complex

摘要

Inspired by a recent successful adiabatic-hindered-rotor treatment for parahydrogen pH_2 in CO_2-H_2 complexes [H. Li, P.-N. Roy, and R. J. Le Roy, J. Chem. Phys. 133, 104305 (2010); H. Li, R. J. Le Roy, P.-N. Roy, and A. R. W. McKellar, Phys. Rev. Lett. 105, 133401 (2010)], we apply the same approximation to the more challenging H_2O-H _2 system. This approximation reduces the dimension of the H _2O-H_2 potential from 5D to 3D and greatly enhances the computational efficiency. The global minimum of the original 5D potential is missing from the adiabatic 3D potential for reasons based on solution of the hindered-rotor Schrdinger equation of the pH_2. Energies and wave functions of the discrete rovibrational levels of H_2O-pH_2 complexes obtained from the adiabatic 3D potential are in good agreement with the results from calculations with the full 5D potential. This comparison validates our approximation, although it is a relatively cruder treatment for pH_2-H_2O than it is for pH_2-CO_2. This adiabatic approximation makes large-scale simulations of H_2O-pH _2 systems possible via a pairwise additive interaction model in which pH_2 is treated as a point-like particle. The poor performance of the diabatically spherical treatment of pH_2 rotation excludes the possibility of approximating pH_2 as a simple sphere in its interaction with H_2O.