[en] Stable isotope ratio measurements provide valuable insights into a broad range of natural processes, from planetary atmospheres and climate to interstellar chemistry. Nitrogen, which has two stable isotopes, exhibits varying isotope ratios across the solar system. To model these observations, the isotope fraction as a function of energy is essential. At the Advanced Light Source (ALS), we measured the photodissociation of molecular nitrogen (N2) with vacuum UV photons where a single photon is sufficiently energetic to dissociate the strong bond. The nitrogen atoms produced are scavenged with H2 to form ammonia, whose isotopic makeup is determined. Blending the experiments with dynamical computations that include the shielding of light, we examine the isotopic composition and electronic atomic states produced. The measured photodissociation of N2 at a natural isotopic composition with a frequency broad light beam exceptionally strongly favors the formation of the heavier nitrogen isotope, 15N. Computations concur and suggest that the maximum in the quantum yield reflects significant variations in the specific electronic quantum states of the product N atoms that have quite different reactivities. Our quantum computations show that at similar energies, photodissociation of 14N14N and 15N14N can lead to different product channels. The computed dynamics include extensive state-selective spin-orbit and nonadiabatic couplings affecting the light absorption and dissociation pathways that proceed via the triplet manifold of states. Our results are relevant for future exploration missions, both in situ and sample-return and for other molecules such as O2 and CO.
Disciplines :
Chemistry
Author, co-author :
Komarova, Ksenia; The Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Gelfand, Natalia A; The Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Remacle, Françoise ; Université de Liège - ULiège > Département de chimie (sciences) > Laboratoire de chimie physique théorique ; The Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Levine, Raphael D ; The Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel ; Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 ; Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
Chakraborty, Subrata; Department of Chemistry and Biochemistry, University of California, La Jolla, CA 92093
Jackson, Teresa L; Department of Chemistry and Biochemistry, University of California, La Jolla, CA 92093
Kostko, Oleg; Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
Thiemens, Mark H ; Department of Chemistry and Biochemistry, University of California, La Jolla, CA 92093
Language :
English
Title :
Photoselective isotope fractionation dynamics of N2 with cosmo and atmospheric chemistry perspectives.
Publication date :
22 July 2025
Journal title :
Proceedings of the National Academy of Sciences of the United States of America
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