EPR study of gamma irradiated arsanilic acid single crystal

Abstract

EPR spectra of gamma irradiated arsanilic acid single crystal shows rarely observed and unstable arsenate centred [(OH)(2)As=O](.) radical. There are two magnetically distinct sites in monoclinic lattice. The principal hyperfine and g values of both sites are determined from spectra taking the large hyperfine effects into account. The principal hyperfine values are found to be A(x)=602, A(y)=437 and A(z)=428 Gauss for one site and A(x)=602, A(y)=438 and A(z)=429 Gauss for the other site. The g values of both sites are the same with the values g(x)=2.048, g(y)=2.001 and g=2.000. The radical is in slightly distorted C-3v symmetry. The unpaired electron is mainly localised on s orbitals of O atoms and partly on p orbital of central As atom. Calculations of EPR parameters for large hyperfine values are discussed and some easily applicable numerical techniques are utilised. (C) 1999 Elsevier Science Ltd. All rights reserved.