APPLICATION OF HIGH-FREQUENCY EPR TO INTEGER SPIN SYSTEMS - UNUSUAL BEHAVIOR OF THE DOUBLE-QUANTUM LINE

A high-frequency EPR study is presented of the integer spin system Ni( II) in the host of Zn-tris(ethylenediamine) dinitrate. This complex sh ows a broad structureless line at X band. At D band (130 GHz) however, a standard triplet powder spectrum is observed. Superimposed on this spectrum is a ''double-quantum'' line at the expected position. The mi crowave power dependency of this line is found to be in contradiction with existing theory on multiple-quantum transitions. The line in our spectra shows a single quantum line behavior in intensity and linewidt h as a function of the microwave frequency from 35 to 130 GHz. A liter ature survey leads to the conclusion that most double-quantum features in high-spin systems do not follow the p(3/2) power dependency predic ted by second-order perturbation theory. In our case the double-quantu m line is assigned to an enhancement effect due to the simultaneous ex citation of two single-quantum transitions. (C) 1998 Academic Press.