# Collisional excitation of NH(3{\Sigma}-) by Ar: A new ab initio 3D potential energy surface and scattering calculations

## TL;DR

This study develops a new 3D potential energy surface for NH-Ar interactions, enabling detailed scattering calculations that improve understanding of molecular collisions relevant to atmospheric and astrophysical environments.

## Contribution

We created a new ab initio 3D potential energy surface for NH-Ar, including NH bond vibration, and performed scattering calculations to determine collisional excitation rates.

## Key findings

- Calculated cross sections for NH-Ar collisions up to 3000 cm-1.
- Derived rate coefficients for temperatures up to 350 K.
- Propensity rules align with similar systems, with some differences.

## Abstract

Collisional excitation of light hydrides is important to fully understand the complex chemical and physical processes of atmospheric and astrophysical environments. Here, we focus on the NH(X3{\Sigma}-)-Ar van der Waals system. First, we have calculated a new three-dimensional Potential Energy Surface (PES), which explicitly includes the NH bond vibration. We have carried out the ab initio calculations of the PES employing the open-shell single- and double-excitation couple cluster method with noniterative perturbational treatment of the triple excitations. To achieve a better accuracy, we have first obtained the energies using the augmented correlation-consistent aug-cc-pVXZ (X = T, Q, 5) basis sets and then we have extrapolated the final values to the complete basis set limit. We have also studied the collisional excitation of NH(X3{\Sigma}-)-Ar at the close-coupling level, employing our new PES. We calculated collisional excitation cross sections of the fine-structure levels of NH by Ar for energies up to 3000 cm-1 . After thermal average of the cross sections, we have then obtained the rate coefficients for temperatures up to 350 K. The propensity rules between the fine-structure levels are in good agreement with those of similar collisional systems, even though they are not as strong and pronounced as for lighter systems, such as NH-He. The final theoretical values are also compared with the few available experimental data.