# Collisional excitation of NH3 by atomic and molecular hydrogen

## TL;DR

This paper presents detailed theoretical calculations of ammonia excitation due to collisions with atomic and molecular hydrogen, providing new rate coefficients and confirming the robustness of the ammonia thermometer in astrophysical observations.

## Contribution

The study offers the first comprehensive set of collisional rate coefficients for NH3 with atomic and molecular hydrogen, expanding previous work limited to helium collisions.

## Key findings

- New rate coefficients for NH3 colliding with H and H2 up to 200 K.
- Significant differences found compared to previous helium-based calculations.
- The ammonia thermometer remains reliable despite different collisional partners.

## Abstract

We report extensive theoretical calculations on the rotation-inversion excitation of interstellar ammonia (NH3) due to collisions with atomic and molecular hydrogen (both para- and ortho-H2). Close-coupling calculations are performed for total energies in the range 1-2000 cm-1 and rotational cross sections are obtained for all transitions among the lowest 17 and 34 rotation-inversion levels of ortho- and para-NH3, respectively. Rate coefficients are deduced for kinetic temperatures up to 200 K. Propensity rules for the three colliding partners are discussed and we also compare the new results to previous calculations for the spherically symmetrical He and para-H2 projectiles. Significant differences are found between the different sets of calculations. Finally, we test the impact of the new rate coefficients on the calibration of the ammonia thermometer. We find that the calibration curve is only weakly sensitive to the colliding partner and we confirm that the ammonia thermometer is robust.