Cr. Timmel et al., A zero-field electron spin resonance spectrometer for the study of transient radical ion pairs, MEAS SCI T, 12(5), 2001, pp. 635-643
A zero-field electron spin resonance spectrometer is described for measurin
g the spectra of spin-correlated radical ion pairs in solution in the frequ
ency range 1-80 MHz. The radical ions are created by continuous optical irr
adiation and rapidly recombine to form an exciplex whose fluorescence is mo
nitored as the radiofrequency is swept, also continuously. The probability
of recombination depends upon the singlet character of the radical pair at
the time that the radicals re-encounter after an initial separation in the
formation step. This is affected directly by resonant state mixing induced
within the radical pair energy manifold by the applied radiofrequency field
. The method yields the spectrum of the radical pair and also allows direct
observation of the effects of radiofrequency radiation on the yields of pr
oducts formed from radical combination reactions.