Sensitivity of mass-independent Sn isotope fractionation to UV radiation and magnetic fields

• 成果类型: Article
• 署名作者: She, Jia - Xin; Li, Weiqiang; Zhang, Shujuan; Gu, Cheng; Chen, Xiru; Zheng, Hongcen; Xu, Cheng; Liu, Wei
• 署名单位: Nanjing University; Nanjing University; Nanjing University; Nanjing University; Nanjing Institute of Environmental Sciences, Ministry of Ecology & Environment
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10109
• DOI: 10.1073/pnas.2504065122
• 发表日期: 2025-06-17
• 关键词: organotin compounds; nuclear volume; sulfur; oxygen; spin; TIN; chondrites; atmosphere; signature; mercury

摘要

Mass-independent isotope fractionation (MIF) enables powerful geochemical tracers for various geological and planetary problems, yet the mechanisms driving MIF for tin (Sn) remain ambiguous. Here, we demonstrate that distinct Sn isotope fractionation signatures were produced during photolysis of organic Sn species (i.e., methyltin) under laboratory UV irradiation and natural sunlight. UV irradiation of methyltin induced pronounced Sn-MIF in all odd Sn isotopes (Delta Sn-115 up to 21.82 parts per thousand, Delta Sn-117 up to 23.16 parts per thousand, Delta Sn-119 up to 24.01 parts per thousand), with their ratios (Delta Sn-117/Delta Sn-115 = 1.069; Delta Sn-119/Delta Sn-115 = 1.099; Delta Sn-119/Delta Sn-117 = 1.028) strongly correlating with nuclear magnetic moments. This unambiguously identifies the magnetic isotope effect (MIE) as the driving mechanism, ruling out other causes such as the nuclear volume effect (NVE). Methyl radicals (center dot CH3) were detectable during the methyltin photolysis experiments, and the magnitude of MIF for Sn was suppressed by the presence of electron spin trapping agent (DMPO) for radicals, supporting that the pronounced Sn-MIF originated from radical-mediated singlet-triplet state transitions of Sn species. Furthermore, the magnitude of Sn-MIF depended nonmonotonically on external magnetic fields (peak suppression at 100 to 180 G), implying competition between hyperfine coupling and Zeeman interactions. Notably, Sn-MIF was absent during photolysis of methyltin by natural sunlight despite significant mass-dependent Sn isotope fractionation (e.g., >3 parts per thousand in delta Sn-122/116), attributed to atmospheric ozone shielding of short-wavelength UV (<290 nm) required for radical generation. Our results register Sn-MIF as a sensitive tracer of UV-driven photochemistry in low-oxygen environments, underlining the potential of Sn isotopes in studies of early Earth's atmosphere and planetary environments.