{\textbf{Rigid rotor state-to-state cross-sections and rates of the PH$_3$+H$_2$ collision}}

Abstract

{Accurate interpretation of observational astronomical data requires reliable collisional rate coefficients for inelasting scattering events between interstellar molecules and the abundant buffer species. An averaged new potential energy surface (PES) for the PH$_3$ symmetric-top molecule in van der Waals (vdW) interaction with H$_2\ ({}^1\Sigma_g^+)$ is generated using quantum chemical methods tooted in the explicitly correlated {CCSD(T)}-{F12} method, in conjunction with the correlation-consistent triple-zeta aug-cc-pVTZ basis sets. Inelastic rotational cross-sections for collisions between \textit{ortho} and \textit{para}-PH$_3$ with \textit{para}-H$_2$ are calculated using the close-coupling quantum scattering method. After Boltzmann thermal averaging, the rate coefficients are evaluated for temperatures up to 100 K. Our results reveal substantial discrepancies between computed PH$_3$-\textit{para}-H$_2$ collisional rates and scaled PH$_3$-He values, underlining the inadequacy of scaling approaches for reliable astrophysical modelling.}