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Nine different potential energy surfaces for CO2–Ar taken from the literature are tested for their ability to reproduce the spectra of the Ar–CO2 van der Waals complex and the pressure broadening of CO2 infrared lines by Ar. None of the potentials give a satisfactory account of all the experimental results. All the potentials are found to give significant discrepancies with at least some of the spectroscopic properties of the van der Waals complex. Coupled-states (CS) and infinite-order sudden (IOS) calculations of the pressure broadening cross sections are compared for a few of the potential energy surfaces. The IOS approximation is found to be seriously inaccurate for some potential surfaces, 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 different potential energy surfaces. For the pressure broadening coefficients, there are substantial uncertainties in the experimental results. Nevertheless, the only potential to give a satisfactory account of the pressure broadening is the electron gas potential of Preston and Pack, which is the least satisfactory of all for the spectra of the complex. It is concluded that a new potential that reconciles the different data sets is needed.

Two potential energy surfaces for CO2–Ar are obtained by least-squares fitting to the high-resolution spectra of Van der Waals complexes and the second virial coefficients of Ar+CO2 gas mixtures. The potentials incorporate a repulsive wall based on monomer ab initio calculations and the assumption that the repulsion potential is proportional to the overlap of the monomer charge densities. The dispersion energy is represented in a two-site model, with dispersion centers located along the C–O bonds of CO2. The resulting potentials give a good representation of all the experimental data with only three or four adjustable parameters. They are quite different from previous empirical CO2–Ar potentials, which all have either a poor representation of the attractive well or a poor representation of the repulsive wall.

Two new potential surfaces for CO2–Ar, obtained principally from the spectra of van der Waals complexes, are tested against measurements of pressure broadening and of transport and relaxation properties, none of which was used in the determination of the surfaces. Pressure broadening of both infrared and Raman lines is considered. The coupled states (CS) approximation is used for all line shape calculations. Thermally averaged infrared and Raman cross sections at 523, 296, 160 and 77 K (infrared) and 295 K (Raman) show good agreement with the experimental data available. Generalized transport and relaxation cross sections are obtained via full classical trajectory and classical CS calculations. Properties tested include diffusion, viscosity and nuclear spin relaxation. They provide a different test of the surfaces and agree well with experiment.

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