Publication: Analytic three-dimensional 'MLR' potential energy surface for CO2-He, and its predicted microwave and infrared spectra

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Title	Analytic three-dimensional 'MLR' potential energy surface for CO2-He, and its predicted microwave and infrared spectra
Authors/Editors*	Hui Li and Robert J. Le Roy
Where published*	Physical Chemistry Chemical Physics
How published*	Journal
Year*	2008
Volume	10
Number
Pages	4128-4137
Publisher	Royal Society for Chemistry
Keywords
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Abstract	A three-dimensional, analytic potential energy surface for CO2-He that explicitly incorporates its dependence on the Q3 asymmetric-stretch normal-mode coordinate of the CO2 monomer has been obtained by least-squares fitting new ab initio, interaction energies to a new three-dimensional Morse/Long-Range (3D-MLR) potential function form. This fit to 2832 points has a root-mean-square (RMS) deviation of 0.032 cm-1 and requires only 55 parameters. The resulting pure ab initio potential provides a good representation of the experimental microwave and infrared data: for 51 pseudo microwave and 49 infrared transition the RMS discrepancies are 0.0110 and 0.0445 cm-1, respectively. Scaling this surface using only two morphing parameters yields an order of magnitude better agreement with experiments, with RMS discrepancies of only 0.0025 and 0.0038 cm-1, respectively. The calculated infrared band origin shift associated with the nu_3 fundamental of CO2 is 0.109 cm-1, in good agreement with the (extrapolated) experimental value of 0.095 cm-1.