Intensity dependence in laser flash photolysis experiments: Hydrated electron formation from ferrocyanide, tyrosine, and tryptophan

The light intensity dependence in monophotonic and consecutive biphotonic processes under laser flash photolysis conditions is derived. In a monophotonic process the relation between photoproduct yield and exciting light intensity is linear but there is saturation at high intensity. In a biphotonic process there are three different regions. The relation is quadratic at low intensity, linear at medium intensity, and there is saturation at high intensity. The difference between the two linear relations is discussed. These results are applied for analyzing the process of hydrated electron formation from excited states of various substances. The process is found to be monophotonic for ferrocyanide. For tyrosine and tryptophan in aqueous neutral solutions, under the conditions of the laser experiments, a biphotonic process is observed. For the tyrosinate ion (alkaline solution pH 12) the findings are not conclusive. Other work on this topic is discussed with reference to the analysis.