Pressure broadening of N2O:He for characterising exoplanetary atmospheres.

Abstract

Nitrous oxide (N2O) is a well studied greenhouse gas present in our atmosphere, it has many known sources on Earth, including production via anaerobic bacteria in soil. N2O had been observed on Mars and is expected to exist in exoplanets. Due to its biological link, it has been proposed as a potential biomarker. The infrared spectrum of N2O has been extensively studied and is well documented and accessible in HITRAN, where the line positions and intensities are vital for the identification of this species in Earth's and other planetary atmospheres. Understanding the impact of dominant gases, however, on the trace species at varying temperatures and pressures is required to accurately quantify the molecular abundances. While the impact of air and selfbroadening of N2O has been thoroughly investigated and is available in the database, the impact of other dominant species is still lacking. Over 5000 exoplanets have been observed with varying sizes, temperatures, pressures, and chemical compositions and it is important to be prepared for a range of different environments. A large portion of these observed planets and the focus of recent JWST-based atmospheric measurements (e.g. Alderson et al. 2023, Tsai et al. 2023, and Bell et al. 2023) are gas-giants, where the dominant species in these atmospheres are H2 and/or He. Minimal experimental data on the broadening effect of H2 and He on N2O is available in the literature, where the work provided by Nakayama et al. 2007 and Tasinato et al. 2010 is not sufficient to provide a sufficient model. Therefore, the broadening coefficients available in HITRAN are currently supplemented using the He broadening coefficients for CO2. We will, therefore, provide the broadening coefficients of N2O with He and H2 using high-resolution infrared spectroscopy to confirm and improve these values. This presentation will focus on the results of N2O broadened by helium.