Linewidths and shifts of very low temperature CO in He: A challenge for theory or experiment?

Abstract

A sensitive capacitance thermometer at low temperature for use in magnetic fields up to 20 T Rev.The pressure broadening and shifting coefficients for pure rotational transitions of CO in a He bath gas at very low temperatures are calculated from the best available potential energy surfaces, and compared with very recent measurements by M. M. Beaky, T. M. Goyette, and F. C. De Lucia ͓J. Chem. Phys. 105, 3994 ͑1996͔͒. The results obtained for two recent empirical potentials determined from fits to Van der Waals spectra, and for a recent high quality purely ab initio surface, are consistent with one another. The best of the spectroscopic potentials also yields good agreement with high temperature virial coefficients and transport properties. Predictions from all three of these potentials agree with linebroadening and shifting measurements at temperatures above ϳ20 K, but are in substantial disagreement with the measurements at temperatures below 4 K. At present, the source of this discrepancy is not known.

Ro-vibrational quenching of CO (v = 1) by He impact in a broad range of temperatures: A benchmark study using mixed quantum/classical inelastic scattering theory

“…[9][10][11][12]28 The improvement of detection techniques 29,30 and development of the PES [31][32][33] went through several refinement cycles. Finally, an acceptable agreement between theory and experiment has been reached in different parts of the desired broad range of temperatures.…”

State to state He–CO rotationally inelastic scattering

“…Thachuk et al gave a thorough review of experimental and theoretical work on He-CO interactions in their 1996 paper. 1 We will give a brief review that concentrates on developments since then and on the work most relevant to the repulsive part of the potential energy surface.…”

“…[12][13][14] Thachuk et al 1 and Dham and Meath 15 subsequently tested the different potentials' predictions against several experimental observables and found that the XC͑fit͒ potential was at least as good as the others.…”

An ab initio potential energy surface for Ne–CO

“…Only the diagonal part of the cross section matrix was used; for the well-isolated 1←0 line and the modest pressures used in the experiment, the off-diagonal ͑intensity transfer͒ terms should not be important. 34 The temperature-dependent cross sections were obtained by thermal averages over cross sections computed at specific energies:…”