D. Whillans, H. Johns
Apr 1, 1969
Photochemistry and Photobiology
Abstract— Photochemical dimerization in orotic acid in aqueous solution has been studied as a function of oxygen concentration, orotic acid concentration and the wavelength of irradiation under two pH conditions. One dimer was detected. Analysis of the data enabled us to obtain a minimum estimate of the efficiency of intersystem crossing, øISC. from singlet to triplet levels. This efficiency increases by a factor of two with increasing energy of excitation over the wavelength range 240–302 nm, and by a similar factor between pH 3 and pH 1. The maximum value obtained was 0.15 for irradiation at 240 nm at pH 1. The relation between quantum yield and øISC is discussed and possible mechanisms to explain this variation of øISC with energy are proposed.