Time resolved magnetic modulation of ion recombination in organic solutions: spin motion in radical ion pairs

Abstract

The evolution of the singlet character of correlated ion radical pairs, prepared by high energy impact (3 particles) in organic liquid and solid solutions, is monitored by nanosecond time resolved solute recombination fluorescence. Results obtained show that the relative variations [I B (t) − I 0 (t)]/I 0 (t) of the luminescence intensity in presence I B (t) and in absence I 0 (t) of magnetic fields (B < 5 kG) decrease exponentially with time, according to a field and solute concentration dependent rate, in liquid but not in solid solutions; in the case of 2b PPD as solute, a damped oscillating component could be observed. The results are interpreted in terms of hyperfine interaction induced coherent singlet–triplet mixing and of field and solute concentration dependent spin–lattice relaxation.