Date of Award
Bachelor of Science
The application of flash photolysis in photochemistry offers an effective means to directly investigate reactive intermediates. This powerful technique rapidly converts a high percentage of molecules in their ground electronic state to upper excited states. This enables the disappearance of the excited species to be observed and kinetic information concerning the rate law and rate constants to be measured. The purpose of our work is to investigate the kinetics of the rate of decay of triplet anthracene in dilute solutions and to obtain rate constants for this reaction. The reduced expression for the decay of triplet anthracene is written: -dT/ dt = k1[T] + kO2 [O2][T]. The radiationless decay constant, k1, is obtained by thoroughly degassing solutions of 5.5x10-4 M anthracene in heptane using a vacuum line. These solutions are flashed and the resulting trace of decay of triplet anthracene, monitored at 424 nm, is measured from an oscilloscope. Values of %T are converted to absorbance and plots for ln At vs time are constructed. Results show that these plots are linear; thus, the reaction follows first-order kinetics. The lowest value of k1 obtained is 4490 sec-1 which is an order of magnitude greater than the literature value 630 sec-1. This indicates that quenching by residual oxygen is occurring and is incorporated in k1 giving kobs = k1 + ko2 [O2]. The quenching rate constant is obtained by adding known aliquots of oxygen to degassed solutions and plotting values of kobs vs. [O2]. The slope of these plots is ko2.
Soltis, Marabeth G., "Flash photolysis: the technique and its application" (1982). Honors Theses. 1886.