Molecular motions in solid U(OCH3)6 as studied by proton spin-lattice relaxation

The temperature dependence of the proton spin-lattice relaxation rate in solid uranium hexamethoxide, U(OCH3)6, has been measured at Larmor frequencies of 30 and 90 MHz. A solid-solid phase transition was located at 161 K. The temperature dependent of the proton relaxation times T1 are interpreted by taking into account the following kinds of motion: CH3 group reorientation about its threefold axis (the O - CH3 vector), a two site jump of the O - CH3 axis (T >161 K) and a continuous rotation of the O - CH3 axis about the U - O vector (T > 161 K). Activation energies and frequency factors for different motion were evaluated. (authors)