The evolution of the singlet character of correlated ion radical pairs, prepared by high-energy impact in alkane solutions, is monitored by nanosecond-time-resolved solute-recombination fluorescence. Results obtained in the presence and absence of magnetic fields ($B<~4$ kG) show evidence for damped periodic modulations ($\omega \approx 10$ MHz) of fluorescence intensity. They are explained in terms of hyperfine-interaction-induced coherent singlet-triplet mixing, and of field-dependent spin-lattice relaxation.

• Received 23 February 1976

DOI:https://doi.org/10.1103/PhysRevLett.36.1214