EVALUATION OF EXISTING POTENTIAL-ENERGY SURFACES FOR CO2-AR - PRESSURE BROADENING AND HIGH-RESOLUTION SPECTROSCOPY OF VAN-DER-WAALS COMPLEXES

Nine different potential energy surfaces for CO2-Ar taken from the lit erature are tested for their ability to reproduce the spectra of the A r-CO2 van der Waals complex and the pressure broadening of CO2 infrare d lines by Ar. None of the potentials give a satisfactory account of a ll the experimental results. All the potentials are found to give sign ificant discrepancies with at least some of the spectroscopic properti es of the van der Waals complex. Coupled-states (CS) and infinite-orde r sudden (IOS) calculations of the pressure broadening cross sections are compared for a few of the potential energy surfaces. The IOS appro ximation is found to be seriously inaccurate for some potential surfac es, especially for high-j lines, so that CS calculations are essential when comparing with experimental line-shape data. CS calculations of line-broadening cross sections are therefore carried out on all nine d ifferent potential energy surfaces. For the pressure broadening coeffi cients, there are substantial uncertainties in the experimental result s. Nevertheless, the only potential to give a satisfactory account of the pressure broadening is the electron gas potential of Preston and P ack, which is the least satisfactory of all for the spectra of the com plex. It is concluded that a new potential that reconciles the differe nt data sets is needed. (C) 1996 American Institute of Physics.