The paramagnetic resonance spectrum of molybdenum in rutile (Ti${\mathrm{O}}_2$) has been studied. The crystal contained 0.05 molar percent molybdenum ions, and the experiments were mainly carried out at 77°K. The observed resonance lines were identified as due to molybdenum in a +5 valence state. The $g$ values in the directions of the three orthorhombic crystal field axes are -1.7883, -1.8117, and -1.9125. The effective orbital $g$ factor, $k$, was calculated to be 0.8784, indicating partial covalent bonding. Hyperfine lines from ${\mathrm{Mo}}^{95}$ and ${\mathrm{Mo}}^{97}$ were also observed, and their hyperfine interaction constants were calculated.

The resonance lines broadened at helium temperature due to saturation of the sample. The spin-lattice relaxation time is very long at this temperature. It increased from 10 to 600 sec as the temperature decreased from 4.2 to 1.3°K.

• Received 11 May 1962

DOI:https://doi.org/10.1103/PhysRev.128.151