Rigid rotor state-to-state cross-sections and rates of the PH ₃ + H ₂ 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 <i>ortho</i> and <i>para</i>-PH₃ with <i>para</i>-H₂ (<i>J</i> = 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-<i>para</i>-H₂ collisional rates and scaled PH₃-He values, underlining the inadequacy of scaling approaches for reliable astrophysical modelling.