Photoselective isotope fractionation dynamics in cosmo and atmospheric chemistry

Photochemical isotope effects have been measured for nearly 50 years with the driving force being the understanding of natural processes. This has ranged from climate and atmospheric chemistry and dynamics, planetary atmospheres such as Mars, Titan and Jupiter, consequences for resolving solar system formation mechanisms, interstellar molecular clouds, solar wind and meteorites. ^1,2 The distribution of isotopomers of compounds varies significantly across the solar system and beyond, invalidating the notion of a constant molecular weight. ³ Nitrogen, with two stable isotopes, exhibits wide-ranging isotope ratios that arise from different sources across the solar system. ^4-11 We seek to understand variability by explicitly examining the dynamics of photodissociation. The paper integrates measurements of photodissociation of N ₂ at the advanced-light-source via scavenging of the nascent N atoms and state of the art dynamics modeling, including preferential light shielding. ^12-14 We show that the exceptionally high nitrogen isotopic fractionation underscores the essential role of dynamics in interpreting photoselectivity and its dominant non-statistical aspects that we establish. High level quantum chemical computations of the relevant potentials and of their different selective couplings that vary in magnitude are vital input towards our demonstrating photoselective chemistry. Beyond N ₂ , our approach is equally applicable for elucidating the isotope ratio reported for CO. ^15,16 The findings support planetary exploration models, including NASA's Artemis missions, where nitrogen isotopic studies of the lunar and Martian surfaces are crucial for understanding water sources and volatile chemistry.