Fundamental approach to the fluence-based kinetic and electrical energy efficiency parameters in photochemical degradation reactions: polychromatic light

When the logarithm of the concentration of a photolyzed component is plotted against the fluence, one usually obtains a first-order plot, and from the slope one can obtain a "fluence-based rate constant". In this study, theoretical expressions are derived for fluence-based rate constants for both monochromatic and polychromatic radiation, and are shown to be fundamental and not dependent on experimental parameters. Therefore, such rate constants can be reproduced from one laboratory to another, as long as the polychromatic light source exhibits similar spectral characteristics. An important quantity that can be obtained from the fluence-based rate constant is the quantum yield. As an example, the quantum yield for the photolysis of atrazine is determined to be 0.033 using the monochromatic fluence-based rate constant. The analysis is extended to the polychromatic light sources, and the expression of polychromatic fluence-based rate constant is derived and validated experimentally for atrazine and NDMA. The new concepts are developed further to analyze the figure-of-merit electrical energy per order (E_EO), and it is shown that the E_EO depends on the same fundamental photochemical parameters. Key words: fluence-based rate constant, quantum yield, UV radiation, fluence rate, kinetics, photochemical parameters.