EPR study of gamma irradiated arsanilic acid single crystal

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 hyperf ine and g values of both sites are determined from spectra taking the large hyperfine effects into account. The principal hyperfine values are found t o 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 t he 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 locali sed on s orbitals of O atoms and partly on p orbital of central As atom. Ca lculations of EPR parameters for large hyperfine values are discussed and s ome easily applicable numerical techniques are utilised. (C) 1999 Elsevier Science Ltd. All rights reserved.