Quantum beats of the reaction yield induced by a pulsed microwave field

The effect of pulsed microwave irradiation on the reaction product has been observed in the photolysis of 2-methyl-1,4-naphthoquinone in a micellar sodium dodecylsulphate solution. Under resonance conditions an increase in the microwave pulse length has resulted in an alternation of the yield of naphthosemiquinone free radicals, due to the periodic population of the reactive singlet state of the radical pair. The singlet–triplet dephasing, induced by long-range interactions between the radicals in the pair, damps the oscillations. The rate constant of this process, obtained from the decrement of the oscillation decay, is (7.1±0.6)×107 s−1.