INFRARED-SPECTRUM AND POTENTIAL-ENERGY SURFACE OF HE-CO

For He-3-CO and He-4-CO van der Waals bimers, fully resolved infrared spectra in the 4.7 mu m region near the fundamental band origin of the CO monomer have been measured for the first time. Only a small fracti on of the observed lines could be assigned using conventional empirica l spectroscopic techniques, and little additional insight was gained f rom synthetic spectra generated from a published ab initio potential f or this system. However, a complete set of unique assignments was made on the basis of comparisons with synthetic spectra generated from a v ariety of trial potential energy surfaces, and least-squares fits to t he observed transition frequencies were used to determine a new anisot ropic potential energy surface for this system. This new surface is mu ch deeper and has a much stronger well depth anisotropy than the best previous one, and its predictions of very low temperature microwave li ne broadening cross sections raise serious questions regarding the met hodology for calculating that property.