Electron spin relaxation of N@C60 in CS2 -: art. no. 014508

We examine the temperature dependence of the electron spin relaxation times of the molecules N@C-60 and N@C-70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero-field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S >= 1 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find an Arrhenius temperature dependence for N@C-60, indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C-70 molecule, which has a permanent ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T-2) ever observed for a molecular electron spin, being 0.25 ms at 170 K. (c) 2006 American Institute of Physics.