2025/12/13 by Ghosh, Priyankush, Rani, Namrata, Yang, Jeehyun +3
#Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM)
paper · doi:10.48550/arxiv.2512.12270
Sulfur chemistry is fundamental to understanding the structure, cloud formation, and atmospheric composition of Venus and Venus-like exoplanets. However, many key reactions involving ground- and excited-state sulfur species remain poorly characterized, and current photochemical models rely on networks that lack accurate kinetic data under high-temperature, high-CO2 conditions. We compute kinetic parameters for reactions of ground-state S(3P) and excited-state S(1D) with CO2 under Venus-like conditions. These reactions form SO(3Sigma), SO(1Delta), and CO. The potential energy surfaces reveal intermediates, and temperature-dependent rate coefficients are obtained using a master-equation approach based on the chemically significant eigenvalue method. NASA 7-term polynomial coefficients are also derived for ground- and excited-state S and SO for consistent use in photochemical models. Incorporating these data into the one-dimensional photochemical model XODIAC shows that these reactions exert only a minor influence above 60 km in the Venus atmosphere due to competing pathways. The model agrees with observations for most sulfur-bearing species except S3 and S4. Introducing a 1 ppm near-surface atomic sulfur mixing ratio, representing a possible deep-atmosphere or surface source or accounting for missing sulfur processes, increases S3 and S4 by 1-2 orders of magnitude and improves agreement with measurements. For exo-Venus analogs with stratospheric isotherms and strong stellar irradiation, the new reactions significantly modify the vertical profiles of major sulfur species above 30 km and enhance S(1D) and SO(1Delta) more strongly than in scenarios with only isotherms or only irradiation. These results underscore the importance of accurate excited-state sulfur kinetics and the need for updated reaction networks when modeling Venus and exo-Venus atmospheres.