Separation of isotropic and anisotropic hyperfine constants in disordered systems by analysis of electron paramagnetic resonance lines at two different microwave frequencies: Application to the molecular structure around excess electrons in γ-irradiated 10M sodium hydroxide alkaline ice glass

Publisher Website
Google Scholar
Abstract
It is shown that the second moment of an unresolved electron paramagnetic resonance line in disordered systems can lead to separation of the isotropic and anisotropic hyperfine couplings if the spectrum is recorded at high enough microwave frequency to separate the main line from nuclear spin flip satellite lines. If resolution of main and satellite lines is not complete, separate determination of the isotropic and anisotropic couplings is still possible if measurement can be made at two different microwave frequencies of which one frequency is high enough to partially resolve the main and satellite lines. This analysis is applied to excess electrons trapped in 10M NaOH alkaline ice glass at 77 K and the isotropic and anisotropic coupling constants are determined as a function of n, the number of equivalent nearest neighbor protons. From electron spin echo modulation patterns and the intensity and separation of satellite lines from the main line, the best value of n is determined to be 6. The value n=6 corresponds to a trapped electron surrounded by three water molecules with their molecular dipoles oriented toward the electron (2 protons per water molecule) or six water molecules with one OH bond oriented toward the electron. In both cases the protons are 2.1 Å from the electron with an isotropic coupling constant of ∼1–2 G. This agrees with independent measurements from analysis of electron spin echo modulation patterns.