Inelastic scattering dynamics of ortho and para hydronium ions, o-HO and p-HO, with He at low temperature.

The hydronium ion, H3O+, presents a crucial key to understanding the chemistry of the interstellar clouds where it has been frequently observed. The present paper is devoted to studying the inelastic scattering of both forms of the hydronium ion, o-H3O+ and p-H3O+, by helium atoms. The interaction potential between H3O+ and He was mapped in Jacobi coordinates leading to a new three dimensional potential energy surface (3D-PES) at the CCSD(T)/aug-cc-pVQZ+BF (CCSD(T)/AVQZ+BF) level of theory. Close coupling treatment was used to obtain rotational cross-sections for both o-H3O+ and p-H3O+ involving 9 rotational states in each case. The cross-sections were computed from energy thresholds up to 500 cm-1 for o-H3O+ and up to 300 cm-1 for p-H3O+, in order to generate rotational rate coefficients for the kinetic temperature range 5-50 K for both forms. The use of the present rates are viewed to be a good tool to estimate hydronium abundance.