ESR line shape studies of trapped electrons in γ-irradiated 17O enriched 10 M NaOH alkaline ice glass: Model for the geometrical structure of the trapped electron

The ESR line shape and width of a trapped electron (et−) has been measured in 34% 17O enriched 10M NaOH alkaline ice glass at 77 K. The second moment of et− due to 17O coupling is 134 G2. Analysis of the second moment contributions from 17O coupling together with the constraint from electron spin echo studies that the et−–O distance is greater than 2 Å show that the et−–17O hyperfine coupling is mainly isotropic. Simulation of the et− ESR line under these constraints on 17O coupling and previous ones determined for H or D coupling for various numbers n of equivalent water molecules in the first solvation shell of et− give a best fit to the experimental line shape for n=6. For n?4 definite structure would be expected in the et− line shape which is not seen experimentally. The n=6 result together with previous data allows a rather complete geometrical description of the trapped, hydrated electron to be defined.