Abstract
The kinetics of formation and decay of acetone ketyl radicals produced by photocleavage of tert-butylperoxide in 2-propanol and the generation of electron spin polarization has been investigated with Fourier-transform electron paramagnetic resonance (FT-EPR). It is found that the evolution of the FT-EPR spectra over a time domain ranging from nanoseconds to 500 μs can be completely explained in terms of: (1) kinetics of radical formation and decay, (2) relaxation of tert-butoxy radical precursors — born with zero spin polarization via the singlet excited state of the peroxide — to thermal equilibrium, (3) spin polarization created by the radical pair mechanism involving random encounters of ketyl radicals (F-pair CIDEP), and (4) spin-lattice relaxation of the ketyl radicals. A detailed numerical analysis of the time dependence of the amplitudes of the central three hyperfine components in the spectrum of the ketyl radical gives a value of 85±30 ns for the spin—lattice relaxation time of the tert-butoxy radical. The analysis also gives the value of the pseudo-first-order hydrogen abstraction rate constant (2.5 × 10 7 s −1) and the magnitude of the F-pair spin polarization.
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