Time-resolved DNP measurements of intermediate free radicals created in the photochemical reaction of benzaldehyde

Abstract

Time-resolved dynamic nuclear polarization (DNP) is measured in the photochemical reaction of benzaldehyde. The creation of nuclear spin polarization is analysed theoretically by a model that includes the cross relaxation, electron spin transition, and chemical reaction of radicals. A comparison between experiment and calculation leads to the following conclusions. (a) The time profile of DNP represents the time dependence of the radical concentration. (b) The rate of cross relaxation affects the intensity of DNP but does not affect its time profile. (c) The cross relaxation rate for the α-proton of the α-hydroxybenzyl radical is one or two orders of magnitude smaller than that for the aromatic protons.