Study of the kinetics and quantum efficiencies in the photochemistry of provitamin D using a tunable laser

An experimental investigation was made of the kinetics of the photoisomerization reactions of provitamin D initiated by a tunable laser at various wavelengths in the 260–305 nm range. The quantum efficiencies of the reversible photoreactions were constant within the provitamin absorption band and substantial changes occurred only when the irradiation was at the long-wavelength wing (λ > 300 nm). In contrast, a nonmonotonic dependence of the quantum efficiencies on the radiation wavelength was exhibited by the irreversible photoreactions.