A room temperature CO$_2$ line list with ab initio computed intensities

TL;DR

This study provides a highly accurate theoretical CO2 line list at room temperature using ab initio methods, crucial for remote sensing applications requiring precise line intensities.

Contribution

It introduces a new ab initio approach to compute CO2 line intensities with uncertainty estimates, improving the accuracy of spectral data for atmospheric monitoring.

Findings

Line intensities match experimental data within 0.5% uncertainty.

The line list covers all relevant transitions below 8000 cm$^{-1}$.

Comparison with HITRAN2012 shows improved accuracy.

Abstract

Atmospheric carbon dioxide concentrations are being closely monitored by remote sensing experiments which rely on knowing line intensities with an uncertainty of 0.5% or better. We report a theoretical study providing rotation-vibration line intensities substantially within the required accuracy based on the use of a highly accurate {\it ab initio} dipole moment surface (DMS). The theoretical model developed is used to compute CO$_2$ intensities with uncertainty estimates informed by cross comparing line lists calculated using pairs of potential energy surfaces (PES) and DMS's of similar high quality. This yields lines sensitivities which are utilized in reliability analysis of our results. The final outcome is compared to recent accurate measurements as well as the HITRAN2012 database. Transition frequencies are obtained from effective Hamiltonian calculations to produce a comprehensive line list covering all $^{12}$C$^{16}$O$_2$ transitions below 8000 cm$^{-1}$ and stronger than 10$^{-30}$ cm / molecule at $T=296$~K