Isotope Effects in Sulfur Recombination Reactions: Preliminary Results from Laboratory Experiments and Implications for Planetary Atmospheres

Abstract:

Recent insights into fundamental mechanisms underlying quadruple stable sulfur isotope (³²S, ³³S, ³⁴S, and ³⁶S) mass‐independent fractionation (S‐MIF) chemistry and potential implications for planetary atmosphere highlight the urgent need of conducting laboratory experiments to delineate the new chemical physics of S‐MIF. We carried out pilot experiments to investigate possible symmetry‐dependent isotope effects in sulfur recombination reactions. We observed small but analytically significant non-zero Δ³³S (0.04‰) and Δ³⁶S (-0.3‰) values in reaction products in one experiment. These values may be too small to characterize S‐MIF processes because reactant and product cannot be effectively separated in our experimental conditions. The S‐MIF signature may have also been diluted by mass‐dependent fractionation components, similar to previous gas‐phase SiO₂ formation experiments, in which a lesser proportion of SiO₂ (via SiO + OH reactions) acquires MIF signatures. Although no definitive statement could be made from only three pilot experiments, it is clear that a full understanding of symmetry‐dependent isotope effects in sulfur recombination reactions in planetary atmospheres is a currently missing component of interpreting S‐MIF signatures in modern aerosols, Archean rocks, and Martian meteorites.