A comprehensive understanding of sulfur chemistry is crucial for the characterization and modeling of planetary atmospheres. The unimolecular decomposition of carbonyl sulfide (OCS + M = CO + S + M) is a critical reaction for the development of accurate photochemical models. In this study, we employ laser absorption spectroscopy (LAS)-based diagnostics in a shock tube to investigate the rate coefficient of OCS decomposition. Sensitive and interference-free diagnostics were developed to monitor OCS depletion at 2070.858 cm-1 and CO formation at 2115.628 cm-1. The reaction rate coefficient of OCS decomposition was measured over a temperature range of 1800-2500 K. This work represents the first experimental determination of OCS decomposition rates in bath gases pertinent to several planetary environments (i.e., He, N2, and CO2). Additionally, we characterize the pressure dependence of the reaction rate through measurements at 1, 2, and 8 atm. The rate constant measured at 2 atm for argon, k1,Ar, aligns with previous studies and is given by k1,Ar = 3.48 × 10-10 exp (-257kJ/RT) cm3 molecule-1 s-1. The relative Chaperone efficiencies at 2 atm were determined as k1,He/k1,Ar = 2.68, k1,N2/k1,Ar = 1.85, and k1,CO2/k1,Ar = 3.67 through our experiments. Our results provide new insights into OCS kinetics, marking the first systematic study of its pressure-dependent behavior in exoplanetary-relevant conditions. These findings, underscored by low experimental uncertainties (±9.0% for k1,Ar, ±12% for k1,He, ±18% for k1,N2, and ±24% for k1,CO2) reflect high-quality, repeatable measurements that will support sulfur chemistry atmospheric modeling and enhance the interpretation of spectroscopic observations from missions such as the James Webb Space Telescope (JWST).
Panda et al. (2026) studied this question.