Nuclear and electron spin relaxation times in a solid nitroxide radical

Abstract

Measurements of the nuclear spin lattice relaxation times of the protons in solid samples of the di-t-butylnitroxide radical have been made. The relaxation times have been measured at different Zeeman frequencies as a function of concentration and of temperature. The primary mechanism for nuclear relaxation in these samples is dipolar coupling between the electron and nuclear spins which is modulated by either electron spin exchange or by electron spin lattice relaxation. Analysis of the N.M.R. data yields the correlation time for the exchange interaction in the concentrated samples and the electron's spin lattice relaxation time in the most dilute samples. Electron-proton separations are also determined from the relaxation data. The correlation time for spin exchange is found to depend strongly on the concentration but to be almost independent of temperature. The electron spin lattice relaxation time exhibits an exponential temperature dependence.