Pressure Broadening Coefficients of SO2 by He for Studies of Exoplanetary Atmospheres

Kurzfassung

Over the past few years, the focus of exoplanetary science has shifted from their detection to the characterization of their atmospheres. A major contributor to this transition has been the James Webb Space Telescope (JWST), which has provided the first detailed constraints on the chemical composition of a wide range of exoplanets, from rocky worlds such as 55 Cnc-e to gas giants like WASP-39b. With the recent first light of GRAVITY+ and upcoming facilities such as ARIEL and the Extremely Large Telescope (ELT), capabilities are expected to improve significantly by delivering spectra with even higher spectral resolution and signal-to-noise ratios.

As a result, the accurate interpretation of these spectra strongly depends on precise spectroscopic reference data, which are typically provided by databases such as HITRAN [1] and ExoMol [2]. While these databases contain extensive molecular line lists and spectroscopic parameters, important data relevant under exoplanetary conditions, particularly pressure-broadening coefficients, are still missing for many species. This limitation becomes especially relevant for molecules such as sulfur dioxide (SO2), which has been discussed as a molecule of astrobiological interest due to its links to geological activity, atmospheric photochemistry, and, in some contexts, potential biosignature scenarios [3,4] in rocky planets. With its detection in the atmosphere of the hot Saturn WASP-39b [5,6], it has been interpreted as the first clear evidence for photochemistry in an exoplanetary atmosphere. Given that H2 and He dominate the atmospheres of gas giants, we focus here on He-induced broadening of SO2 as a collisional partner for interpreting these atmospheres over a relevant pressure range (up to 1 bar).

We perform high-resolution gas-phase spectroscopy using a Bruker 120/5 HR FTIR spectrometer in the mid-infrared spectral region. In particular, we determine pressure-broadening coefficients of SO2 at room temperature for pressures up to 1000 mbar. In this talk, I will present first results on He-induced pressure broadening of SO2, focusing on the v3 and v1+v3 bands, and compare them with existing values in the HITRAN database.

References:

[1] Gordon et al. 2026, JQSRT 353, 109807

[2] Tennyson et al. 2016, J. Mol. Spectrosc. 327, 73

[3] Seager et al. 2016, Astrobiology, 16(6), 465

[4] Schwieterman et al. 2018, Astrobiology, 18(7), 663

[5] Alderson et al. 2023, Nature, 614, 664

[6] Rustamkulov et al. 2023, Nature, 614, 659