Electric quadrupole transitions in carbon dioxide

TL;DR

This paper provides accurate theoretical predictions of the complete quadrupole ro-vibrational spectrum of CO₂, validated by recent measurements, aiding atmospheric and astrophysical detection of weak quadrupole transitions in planetary atmospheres.

Contribution

It offers the first comprehensive theoretical prediction of CO₂ quadrupole spectra, validated by experiments, enhancing understanding of weak spectral features in planetary atmospheres.

Findings

Validated predictions with recent spectroscopy measurements.

Identified quadrupole transitions in key atmospheric transparency regions.

Enabled improved detection of CO₂ in planetary atmospheres.

Abstract

Recent advances in the high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe for the first time very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here we present accurate theoretical predictions of the complete quadrupole ro-vibrational spectrum of a non-polar molecule CO$_2$, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars ACS MIR spectroscopic observations of the martian atmosphere. Predicted quadrupole transitions appear in some of the mid-infrared CO$_2$ and water vapor transparency regions, making them important for detection and characterization of the minor absorbers in water- and CO$_2$-rich environments, such as present in the atmospheres of Earth, Venus and Mars.