Interaction of H2O with CO: potential energy surface, bound states and scattering calculations

Abstract

Collisions between H₂O and CO play a crucial role in the gaseous component of comets and protoplanetary disks. We present here a five-dimensional potential energy surface (PES) for the H₂O–CO collisional complex. Ab initio calculations were carried out using the explicitly-correlated closed-shell single- and double-excitation coupled cluster approach with the non-iterative perturbative treatment of triple excitations [CCSD(T)-F12a] method with the augmented correlation-consistent aug-cc-pVTZ basis sets. The most stable configuration of the complex, where the carbon atom of CO is pointing towards the OH bond of water, has a binding energy D_e = 646.1 cm⁻¹. The end-over-end rotational constant of the H₂O–CO complex was extracted from bound state calculations and it was found to be B₀ = 0.0916 cm⁻¹, in excellent agreement with experimental measurements. Finally, cross sections for the rotational excitation of CO by H₂O are computed for s-wave (J = 0) scattering at the full close-coupling level of theory. These results will serve as a benchmark for future studies.