EPR and optical absorption studies on VO2+ ions in calcium fumarate trihydrate single crystals

Electron Paramagnetic Resonance (EPR) studies of VO2+ ions in calcium fumarate trihydrate single crystals have been done at room temperature. EPR analysis indicates the presence of two magnetically inequivalent VO2+ sites. For the two sites the spin Hamiltonian parameters are, Site I: gx = 1.9689, gy = 2.0087, gz = 1.9344, Ax = 73, Ay = 88, Az = 202; Site II: gx = 1.9675, gy = 2.0100, gz = 1.9346, Ax = 75, Ay = 90, Az = 206 (×10−4) cm−1. The optical absorption study is also carried out at room temperature. By correlating EPR and optical data the nature of bonding in the crystal is discussed. The three-line superhyperfine structure has been attributed to two protons.