CHEMICALLY-INDUCED DYNAMIC ELECTRON POLARIZATION (CIDEP) IN MODERATELY FAST-RELAXING SYSTEMS

The relative intensities of individual hyperfine lines in the radical pair mechanism spin-polarized electron spin resonance spectrum of a ra dical are imperfectly calculated using standard theory, especially whe n the counter-radical undergoes fast relaxation. Here an approximate t reatment valid in moderately fast relaxing systems is given in which t he origin of the effect is treated as a Lorentzian distribution of spi n mixing frequencies. This corresponds broadly to considering them to be determined by the lineshape of the electron spin resonance (ESR) sp ectrum of the counter-radical. The approach is shown to provide an ade quate basis for simulation of the spin polarized spectrum of the hydro xymethyl radical produced, along with a fast relaxing acyl radical, on photolysis of hydroxypropanone. In principle it provides a measure of the relaxation time of the acyl through observations on hydroxymethyl . With ESR lines of normal linewidth any correction to existing theory is usually negligible within experimental accuracy.