Nanosecond laser photolysis of provitamin D

The energy and spectral dependences of laser photoisomerization of provitamin D were investigated. When photolysis was initiated by XeCl laser radiation, there was a major change in the reaction causing suppression of the formation of the main photoproducts and irreversible photodegradation of the original substance. Theoretical and experimental studies demonstrated that two-photon photoprocesses were not involved in the observed "anomalous" behavior of the reaction. An investigation of the kinetics of the photoreaction caused by excitation in the 280–305 nm range, provided by tunable lasers, revealed a significant increase in the role of irreversible phototransitions in provitamin D as a result of irradiation corresponding to the long-wavelength edge of the absorption band.