Dosimetry in Photochemistry*

A method of dosimetry which is useful in analyzing complex photochemical reactions involving more than one photoproduct is described. This involves determining a photochemical cross section for each of the products, σ B , σ c … ., and an absorption cross section σ. for the reacting species. The ratio σ B /σ a is the quantum yield for production of product B . Where a number of photoproducts are produced simultaneously, it is convenient to express ‘dose’ in terms of the average number of photons per cm 2 ‘seen’ by each molecule in the vessel. This average can be calculated from the number of incident photons, the volume of the liquid, the absorbance and the path length. Experimental details of the irradiation facility which is convenient for such studies are presented. The method of dosimetry is illustrated using photochemical data for uracil and orotic acid in solution.