Collisional excitation of HD by H

Abstract

ABSTRACT The HD molecule plays an important role in many astrophysical environments. Accurate modelling of the gas cooling induced by HD and its abundance in such media requires a proper modelling of its excitation by both radiative and collisional processes. Reliable state-to-state collisional rate coefficients in extended temperature regimes are then essential to allow for the description of different astrophysical environments where deviations from local thermodynamic equilibrium regime can occur. Here, we report exact quantum time-independent reactive scattering calculations for the rovibrational excitation of HD by H. Rate coefficients are computed for temperatures up to 5000 K and transitions between all rovibrational states with internal energies up to 14 000 cm−1. Previous results neglecting reactive and exchange channels of the colliding system are compared to the new ones and significant differences are found. The present work represent a big step in the complete description of the HD–H collisional system, in terms of rovibrational states considered, temperature range explored and accuracy. Hence, we recommend the use of the new HD–H collisional data presented here to accurately model the astrophysical environments where HD plays a role.