High-Resolution Infrared Spectroscopy of N2O and SO2 Broadened by Helium to Assist in Analysis of Exoplanetary Atmospheres

Abstract

The James Webb Space Telescope (JWST), launched in 2021, as well as the next generation telescopes like Extremely Large Telescope (ELT), ARIEL, and GRAVITY+, will collect high resolution spectral data of exoplanetary atmospheres with high sensitivity, covering the near to mid-IR, and optical regions of the electromagnetic spectrum. The interpretation of these spectra requires accurate line modeling based on reference laboratory data, including transition frequencies, line intensities, and broadening parameters along with their temperature dependence. These molecular parameters are available in databases such as HITRAN [1,2] and EXOMOL [3] to aid in modeling and interpreting the spectra of planetary atmospheres. However, many key parameters in these spectral catalogs remain incomplete. In particular, pressure and temperature dependent broadening parameters of several molecules relevant to exoplanetary atmospheres, such as, N2O, SO2, and OCS, in He-, H2-, and CO2-dominated environments are limited. For example, previous experimental work on the pressure broadening of N2O by He, reported by Tasinato et al. [4] and by Nakayama et al. [5], is not enough to allow a fit to build a sufficient model for it [6]. Therefore, it becomes essential to have a complete set of pressure and temperature based broadening parameters for such molecules in foreign broadening gases. In this study, we present high-resolution infrared measurements of N2O and SO2 broadened by He. N2O is a potential biosignature gas, while SO2 is one of the photochemical products that was also recently identified in exoplanetary atmospheres, e.g. WASP39-b [7,8]. Using a Bruker IFS 120/5HR spectrometer with a spectral resolution of 0.002 cm-1, we investigate the pressure broadening effects of He on N2O, and SO2 at room temperature, with pressures up to 1000 mbar. These measurements aim to enhance existing spectral databases and support the accurate characterization of exoplanetary atmospheres. [1] Gordon, I. E., Rothman, L. S., Hargreaves, E. R., Hashemi, R., Karlovets, E. V., Skinner, F. M., Conway, E.K., et al., 2022 J. Quant. Spectrosc. Radiat. Transfer, 277, 107949 [2] Tan, Y., Skinner, F. M., Samuels, S., Hargreaves, R. J., Hashemi, R., and Gordon, I. E. 2022 The Astrophysical Journal Supplement Series 262(2), 40 [3] Tennyson, J., Yurchenko, S.N., Zhang, J., Bowesman, C.A., Brady, R.P., Buldyreva, J., Chubb, K.L., Gamache, R.R., Gorman, M.N., Guest, E.R. and Hill, C., 2024 J. Quant. Spectrosc. Radiat. Transfer, 326, 109083 [4] Tasinato, N., Hay, K. G., Langford, N., Duxbury, G., & Wilson, D., 2010 J. Chem. Phys., 132, 16 [5] Nakayama, T., Fukuda, H., Sugita, A., Hashimoto, S., Kawasaki, M., Aloisio, S., Morino, I. and Inoue, G., 2007 Chem. Phys., 334(1-3), pp.196-203 [6] Tan, Y., Skinner, F. M., Samuels, S., Hargreaves, R. J., Hashemi, R., and Gordon, I. E. 2022 The Astrophysical Journal Supplement Series 262(2), 40 [7] Rustamkulov, Z., Sing, D.K., Mukherjee, S., May, E.M., Kirk, J., Schlawin, E., Line, M.R., Piaulet, C., Carter, A.L., Batalha, N.E. and Goyal, J.M., 2023 Nature, 614, 7949 [8] Alderson, L., Wakeford, H.R., Alam, M.K., Batalha, N.E., Lothringer, J.D., Adams Redai, J., Barat, S., Brande, J., Damiano, M., Daylan, T. and Espinoza, N., 2023 Nature, 614, 7949