Longitudinal spin lattice relaxation time of the uranyl phenanthraquinone radical ion complex

The longitudinal spin lattice relaxation time T1 for the uranyl phenanthraquinone radical complex ion (UO2PQ)/sup +./ is much less than that for the phenanthraquinone radical anion PQ/sup -./. A qualitative understanding of the effect is achieved by recognizing that the U atom has an enormous spin--orbit coupling. A calculation which includes the U 5f/sub plus-or-minus2/ (5f/sub z/,x2/sub -y/2 and 5f/sub z/xy) orbitals in the π system provides a semiquantitative understanding but the formal charge of U is closer to +1 than to +2. The state of the odd electron is described by a Huckel approach and the description of T1 includes G tensor modulation and spin--rotation interaction