Collisional excitation of singly deuterated ammonia NH_2D by H_2

Abstract

The availability of collisional rate coefficients with H_2 is a pre-requisite for interpretation of observations of molecules whose energy levels are populated under non-local thermodynamical equilibrium conditions. In the current study, we present collisional rate coefficients for the NH2D/para-H_2(J2 = 0, 2) collisional system, for energy levels up to J_τ = 7_7 (E_u ∼ 735 K) and for gas temperatures in the range T = 5–300 K. The cross-sections are obtained using the essentially exact close-coupling (CC) formalism at low energy and at the highest energies, we used the coupled-states (CS) approximation. For the energy levels up to Jτ = 42 (E_u ∼ 215 K), the cross-sections obtained through the CS formalism are scaled according to a few CC reference points. These reference points are subsequently used to estimate the accuracy of the rate coefficients for higher levels, which is mainly limited by the use of the CS formalism. Considering the current potential energy surface, the rate coefficients are thus expected to be accurate to within 5 per cent for the levels below J_τ = 42, while we estimate an accuracy of 30 per cent for higher levels.

Files

Additional details