A new, fully ab initio investigation of the NO(X 2Π)Ar system. I. Potential energy surfaces and inelastic scattering

We report new coupled-cluster [CCSD(T)] ab initio calculations of the two potential energy surfaces (PES’s) of the Ar–NO complex. Successively larger basis sets are used to extrapolate to the complete basis set limit. Although qualitatively very similar to our earlier PES’s [M. H. Alexander, J. Chem. Phys. 99, 7725 (1993)], the new PES’s have substantially deeper wells ${\mathrm{(D}}_e\text{=116\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}\mathrm{).}$ Full close-coupled integral inelastic cross sections were determined at collision energies of 442 and 1774 cm⁻¹ for transitions out of the lowest NO rotational level $\text{(j=ω=1/2).}$ For transitions into higher rotational levels of the same spin–orbit manifold the cross sections are little changed from previously calculated values, and still in some disagreement with recent experiments. For transitions in which the spin–orbit manifold changes (ω=1/2→3/2), the calculated integral cross sections are larger than the previously calculated values at $\text{E=442\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ but agree quite closely at $\text{E=1774\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}.$ At both energies, however, the calculated cross sections for spin–orbit changing transitions are noticeably smaller than experimentally derived values.