Laser photosynthesis of previtamin D: new effects of high-intensity picosecond irradiation

An investigation was made of the influence of the intensity of picosecond (τ_p ≈ 23 ps) laser pulses on the kinetics of the photosynthesis of previtamin D₃. An increase of the intensity from 10¹² to 10¹⁴ W m^–2 resulted in significant changes in the photosynthesis kinetics: the photoreaction rate fell and so did the efficiency of the cis–trans isomerisation of previtamin D. An analysis showed that two-step absorption made only a small contribution to these effects and that they were mainly associated with the excitation of nonequilibrium conformers of the previtamin molecule.