Infrared spectrum and potential energy surface of He–CO

Abstract

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

State-to-state rotational rate constants for CO+He: Infrared double resonance measurements and simulation of the data using the SAPT theoretical potential energy surface

“…In 1994 McKellar and Chan published a highresolution infrared spectrum of the He-CO van der Waals complex. 15 Their experiment was later extended in both the IR 16 and microwave [17][18][19] regions. The spectroscopic data made it clear that the TKD description of the He-CO attractive well was inadequate.…”

State to state He–CO rotationally inelastic scattering

“…10 The TKD potential was unable to explain the observed spectrum, so McKellar et al developed a new empirical surface, called V (3,3,3) , by fitting an analytic model to the spectrum. Le Roy et al then fitted a different potential model, the exchange-Coulomb ͑XC͒ model, to the same spectrum and obtained equally good agreement with the spectroscopic observations.…”

An exchange-Coulomb model potential energy surface for the Ne–CO interaction. I. Calculation of Ne–CO van der Waals spectra

“…It was found, 23 however, not to predict the experimental rovibrational energy levels of the 4 He - 13 C 16 O isotopolog as accurately as the V ͑3,3,3͒ PES of Ref. 17.…”

“…The He-CO XC͑fit͒ PES not only provides an excellent fit to the positions of the IR spectral lines of the He-CO dimer but also predicts the various transport properties of He-CO bulk gas mixtures better than other available high-quality PESs, such as the V ͑3,3,3͒ PES of Chuaqui et al 17 and the symmetry-adapted perturbation theory ͑SAPT͒ PESs of Moszynski et al 18 and Heijmen et al 19 ͑see Refs. 20-22͒.…”