QUANTUM MONTE-CARLO SIMULATIONS OF AR-N-CO2 CLUSTERS

Potential-energy functions for CO2-Ar-n clusters are constructed using the pairwise-additive approximation from the Ar-Ar potential of Aziz [J. Chem. Phys. 99, 4518 (1993)] and three different CO2-Ar potentials which have been reported recently. These are used to find minimum-ene rgy structures and to carry out rigid-body diffusion Monte Carlo simul ations of the ground vibrational state for CO2-Ar-n clusters with n up to 30, as well as the first excited state for n = 1. From these resul ts, the CO2 nu(3) redshift is estimated. For all values of n, the Ar a toms tend to surround the CO2 molecule. A complete first solvation she ll is first found for n = 14, and the largest complete first salvation shell is found for n = 17. Although the most recent semiempirical CO2 -Ar potential function of Hutson et al. [J. Chem. Phys. 105, 9130 (199 6)] gives more accurate predictions of spectroscopic properties for n = 1 than the best available ab initio potential function [Marshall et al., J. Chem. Phys. 104, 6569 (1996)], both potential functions give q uite similar predictions for structures and approximate CO2 nu(3) reds hifts for larger values of n. (C) 1998 American Institute of Physics.