A Phenomenological Description of Electron Paramagnetic Double-Resonance Relaxation of Organic Free Radicals in Solution. II. ENDOR Relaxation of Galvinoxyl

Abstract

Abstract The ratio of the ENDOR enhancement to the ESR intensity (E) of galvinoxyl in toluene was measured under various conditions of microwave power, rf power and temperature. The results are discussed in comparison with a phenomenological theory in part I. It is proven that the apparent longitudinal electron spin relaxation time for a t-butyl proton under NMR excitation is about twice as long as those for methylidyne and ring protons, which is explained by the effect of incomplete hf separation. Also, it is shown that the reciprocal of the slope of the plot of E−1 vs. (rf power)−1 for methylidyne and ring protons is approximately proportional to the number of equivalent protons, whereas that for a t-butyl proton can be explained only if the effect of incomplete hf separation is taken into consideration. The value of b=Wn⁄We for methylidyne and ring protons, simulated from the temperature dependence of E based on a previous theory, can be closely correlated to the spin distribution in galvinoxyl.