Electron paramagnetic resonance studies of VO²⁺ in single crystals of NaCl, KCl and RbCl

Abstract

Electron paramagnetic resonance (EPR) of VO²⁺ radicals incorporated in face-centred single crystals of NaCl, KCl and RbCl has been studied in the temperature range of 77^° K to 330^° K. At liquid nitrogen temperature, anisotropic spectra have been recorded in each case while spectra recorded at room and higher temperatures are isotropic suggesting the existence of a fast readjustment of VO²⁺ molecular ions in the crystals at higher temperature while this motion gets hindered at liquid nitrogen temperatures. Spin-Hamiltonian constants are calculated from the recorded isotropic and anisotropic spectra. The line widths in each case are found to obey a parabolic law originally proposed by Kivelson. The constants which give a close fit have been evaluated. The random orientation and readjustment of V-0 bond in these alkali chloride crystals is explained on the assumption that the medium exhibits a "liquid-like" nature for VO²⁺ molecular ion as far as the electron paramagnetic resonance absorption is concerned.