NMR-STUDY OF GEMINATE RECOMBINATION OF RADICALS IN LIQUID SOLUTION - COMPLEMENTARY USE OF SCOTCH AND PHOTO CIDNP EXPERIMENTS

A 2D NMR experiment, SCOTCH (spin coherence transfer in chemical react ions), is used to study the kinetics of a geminate radical pair in liq uid solution. If an rf pulse is followed by a laser pulse that creates radical pairs transverse nuclear magnetization is transferred from st arting material to products. The intensity of this magnetization can b e reduced by dephasing processes due to the hyperfine coupling with th e free electron in the radical. A theoretical expression for this decr ease is given in terms of the lifetime of the radical and the hyperfin e coupling constant. Application to the photochemical reaction of pina colone (methyl t-butylketone) in tetrachloromethane, supplemented with time resolved CIDNP measurements, led to an average lifetime of about 3 ns for the geminate radical pair and 0.4 mus for the escaping radic als.