Hydrogen atom in γ-irradiated synthetic isopropylamine silica clathrate

Abstract

Silica clathrates have polyhedral cage structures with guest molecules and are naturally found under various forms such as melanophlogite, chibaite, or bosoite. Although electron spin resonance (ESR) could be potentially used to date their formation, the evaluation of the thermal stability of the radiation-induced radicals is not simple, like in the case of chibaite. Decay mechanism of the radical should be understood to ensure reliable ESR dating results. To investigate the behavior of radiation-induced radical in silica clathrate, isopropylamine silica clathrate was synthesized from mixed solutions of orthosilicic acid and isopropylamine. Hydrogen atom and (CH3)2C·(NH2) radical are mainly formed by γ-ray irradiation at 77 K. Hydrogen atom decay around 230 K by following a first-order kinetics and its activation energy is 65 ± 4 kJ/mol. Since the amount of hydrogen atom decrease was similar to that of the (CH3)2C·(NH2) radical increase, it is hypothesized that hydrogen atom abstracts hydrogen from isopropylamine in the silica clathrate.