Collisional excitation of singly deuterated ammonia NH$_2$D by H$_2$

TL;DR

This study provides new collisional rate coefficients for NH₂D interacting with para-H₂ across a wide temperature range, essential for interpreting astrophysical observations under non-LTE conditions.

Contribution

It presents the first comprehensive set of collisional rate coefficients for NH₂D with H₂ up to high energy levels and temperatures, using advanced quantum scattering methods.

Findings

Rate coefficients are accurate within 5% for levels below Jτ=4_2.

Estimated accuracy for higher levels is about 30%.

Data covers energy levels up to Jτ=7_7 and temperatures 5-300K.

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 NH$_2$D / para--H$_2$($J_2 = 0,2$) collisional system, for energy levels up to $J_\tau = 7_7$ ($E_u$$\sim$735 K) and for gas temperatures in the range $T = 5-300$K. The cross sections are obtained using the essentially exact close--coupling (CC) formalism at low energy and at the highest energies, we used the coupled--states (CS) approximation. For the energy levels up to $J_\tau = 4_2$ ($E_u$$\sim$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\% for the levels below $J_\tau = 4_2$, while we estimate an accuracy of 30\% for higher levels.