Pairs of radical ions are generated in polar solvents by nanosecond laser flashes in a singlet electron spin state via photoinduced electron transfer. The recombination monitored spectroscopically with a time resolution ~ 3 ns can be resolved into a fast geminate (~ 10 ns) and a slow homogeneous (~ 1000 ns) process. It has been observed for the system pyrene + 3, 5-dimethoxy-dimethylaniline in methanol that triplet products appear already during the geminate phase of the recombination. The yield of these fast triplet products is reduced by an external magnetic field of 500 Gauss to about 80% of its zero field value. The magnetic field dependence of this effect in the range 0–500 Gauss has been measured under stationary conditions. The results are found to be in agreement with a theoretical model based on the assumption that the change of spin multiplicity of the initial radical pairs originates from the hyperfine coupling between unpaired electron spins and nuclear spins within each radical.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry