N2– and (CN)2– spin-lattice relaxation in KCN crystals

Abstract

The spin-lattice relaxation rates of the anionic substitutional radicals N₂^– and (CN)₂^– produced by X-rays in potassium cyanide crystals have been determined by e.s.r. continuous-wave saturation techniques. Measurements taken in the temperature range 10–80 K have shown that for both centres the temperature dependence of the spin–lattice relaxation rate can be expressed as a sum of two exponential terms. The characteristic energies associated with this dependence are very close to the measured transition energies of CN^– librational levels, which are strongly coupled to translational modes of the lattice. Owing to the static and dynamic similarities of the paramagnetic centres with the normal (CN)^– anions of the lattice, we suggest a coupling mechanism between the spin states of the molecular species and their librational modes, giving rise to the observed temperature dependence through an Orbach-like relaxation process.