EPR and optical absorption studies on VO 2+ ions in l-asparagine monohydrate single crystals

Abstract

X-Band electron paramagnetic resonance (EPR) studies of VO 2+ ions in l-asparagine monohydrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO 2+ sites. Both the vanadyl complexes are found to take up interstitial position. The angular variation of the EPR spectra in three planes ab, bc and ca are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, site I: g x = 1.9633, g y = 2.0274, g z = 1.9797, A x = 88, A y = 61, A z = 161 × 10 −4 cm −1; site II: g x = 1.9627, g y = 1.9880, g z = 1.9425, A x = 90, A y = 66, A z = 167 × 10 −4 cm −1. The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.