ExoMol line lists -- XL. Ro-vibrational molecular line list for the hydronium ion (H$_3$O$^+$)

TL;DR

This paper presents a comprehensive and accurate ro-vibrational line list for hydronium (H$_3$O$^+$), based on new ab initio calculations and empirical data, enabling better detection in planetary and exoplanet spectra.

Contribution

It introduces the first extensive and precise line list for H$_3$O$^+$ covering a wide spectral range up to 10,000 cm$^{-1}$, combining ab initio and empirical methods.

Findings

Line list covers up to 10,000 cm$^{-1}$ (wavelengths >1 μm).

Complete for temperatures up to 1500 K.

Publicly available for spectral analysis.

Abstract

A new line list for hydronium (H$_3$$^{16}$O$^+$) is computed. The line list is based on a new ab initio dipole moment surface (CCSD(T)/aug-cc-pVQZ) and a new empirical potential energy surface (PES). The empirical PES of H$_3$O$^+$ was obtained by refining an ab initio surface through a global fit to the experimentally determined ro-vibrational energies collected from the literature covering the ground, $\nu_1^{\pm}$, $\nu_2^{\pm}$, $2\nu_2^{\pm}$, $\nu_3^{\pm}$ and $\nu_4^{\pm}$ vibrational states. The line list covers the wavenumber range up to 10 000 cm$^{-1}$ (wavelengths $>1 \mu$m) and should be complete for temperatures up to $T=1500$ K. This is the first comprehensive line list for H$_3$O$^+$ with extensive wavenumber coverage and accurate transitional probabilities. Prospects of detection of hydronium in spectra of solar system giant planets as well as exoplanets are discussed. The eXeL line list is publicly available from the ExoMol and CDS databases.