Spin Exchange in Solutions of di-Tertiary-Butyl Nitroxide

The ESR linewidths of dilute solution of di-tertiary-butyl nitroxide (DTBN) in n-pentane and propane have been studied. Corrections have been made for (1) spin-rotational effects, (2) the variation of concentration with temperature, (3) the line-shape distortion of overlapping “strongly exchanging” lines, (4) the exchange narrowing of inhomogeneous linewidth contributions arising from proton extra hyperfine splitting, and (5) the temperature dependence of the diffusional step length λ. Existing theories of spin exchange appear adequate to explain the low-concentration data; at high concentration it is not possible to make all the corrections discussed above and the comparison of theory and experiment is not meaningful. In n-pentane we found that (zT/z).Jλ02 = 5×1012 Å2 sec−1 and JzT = 4.9×1011 sec−1, where J is minus two times the exchange integral, λ0 is the diffusional step length at the freezing point, zT is the mean total number of molecular nearest neighbors, and z is the number of new radical nearest neighbors encountered in each jump. The results for DTBN in propane are similar.