EPR and a b i n i t i o SCF–MO studies of the Si⋅H–Si system in the E′4 center of α-quartz

Abstract

The E′4 center in irradiated α-quartz has been studied by single-crystal EPR. The unpaired electron is shared mainly by two silicon ions Si(1, 2) with the larger fraction on Si(2). The spin-Hamiltonian parameter matrices ḡ, Ā1H, Ā29Si(1, 2) at 40 K, as well as Ā29Si(1, 2) at 300 K, are reported. A model of the E4′ center, consisting of an O− vacancy between Si(1, 2), with a hydride ion bonded to Si(1), is presented. Ab initio SCF–MO calculations for a 15-atom cluster, yielding the minimum energy atom configurations, have supported this model by giving good qualitative agreement with the EPR data. The temperature dependence of the hyperfine matrices Ā29Si(1, 2) is explained by Boltzmann population of the vibrational levels in the asymmetric double-minimum potential of the hydrogen bond system Si(2) ⋅ H–Si(1).