An ESR and ENDOR study of irradiated ⁶Li-formate

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• 作者：K. Komaguchi ; Y. Matsubara ; M. Shiotani ; H. Gustafsson ; E. Lund ; A. Lund
• 关键词：⁶Li-formate ; CO₂⁻ ; radical anion ; ESR ; ENDOR
• 刊名：Spectrochimica Acta Part A ; Molecular and Biomolecular Spectroscopy
• 出版年：2007
• 期刊代码：99_13861425
• 类别：ch
• 出版时间：March 2007
• 卷：66
• 期：3
• 页码：754-760
• 文件大小：547 K

摘要

Lithium formate (⁶LiOOCH·H₂O), 95%⁶Li enrichment, combined with an exchange of crystallization water with D₂O was investigated. The ESR spectrum of the radiation induced free radicals stable at room temperature consists of a singlet with a narrow line width, 0.92 mT. ⁶Li has smaller magnetic moment and nuclear spin, which resulted in the narrower line width accompanied with an increase in peak amplitude. In comparison with lithium formate with natural isotopic composition, ⁶Li (7.5%, I = 1) and ⁷Li (92.5%, I = 3/2), the sensitivity was increased by a factor of two. With optimised spectrometer settings ⁶Li formate had seven times higher sensitivity compared to alanine. Therefore this material is proposed as a dosimeter material in a dose range down to 0.1 Gy. The g and the ¹³C-hyperfine (hf) tensors of the CO₂⁻ radical anion, major paramagnetic products, were evaluated to be g = (2.0037, 1.9975, 2.0017), and A(¹³C) = (465.5, 447.5, 581.3) MHz for polycrystalline samples at room temperature. Furthermore, the ¹H-hf and ⁶Li-hf tensors observed for the surroundings of CO₂⁻ by ENDOR technique were in fairly good agreement with DFT calculations. The CO₂⁻ radicals are found to be so stable that the formate is applicable to the ESR dosimetry, because of fully relaxing in a fully relaxed geometrical structure of the CO₂⁻ component and remaining tight binding with the surroundings after the H atom detachment from HCO₂⁻.