Rigid rotor state-to-state cross-sections and rates of the PH₃ + H₂ collision

Accurate interpretation of observational astronomical data requires reliable collisional rate coefficients for inelasting scattering events between interstellar molecules and the abundant buffer species. A five-dimensional potential energy surface (PES) for the PH₃ ( ¹A₁) – H₂ (¹Σ⁺g) interaction was generated using the explicitly correlated CCSD(T)-F12 method in conjunction with the correlation-consistent triple-zeta aug-cc-pVTZ basis set, and averaged over H₂ orientations to yield a reduced three-dimensional surface. Inelastic rotational cross-sections for collisions between ortho and para-PH₃ with para-H₂ (J = 0) 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 PH₃-para-H₂ collisional rates and scaled PH₃–He values, underlining the inadequacy of scaling approaches for reliable astrophysical modelling.