Application of semiconductor diode lasers to probe photodissociation dynamics

In the present study on the photodissociation of alkyl iodides, we utilize a recently developed technique1 of laser gain-vs-absorption spectroscopy to obtain accurate quantum yields. The laser gain-vs-absorption approach, which is a two-laser pulse-and-probe technique, obtains quantum yields from a single time-resolved transient. The initial population inversion following photolysis and the total absorption after complete quenching of the excited state species are measured on a short (~10-μs) time scale. Due to the nature of the internal normalization of the measurement, most experimental parameters cancel, and very accurate results can be obtained. In this work, gain-vs-absorption measurements are per formed with a room temperature InGaAsP diode probe laser. Quantum yields determined at 266 nm for n-C3F7I, i-C3F7I, and CH3I are 102 ± 4%, 102 ± 7%, and 73 ± 4%, respectively. The results are in good agreement with the majority of earlier works, except for recent photoacoustic measurements which gave much lower values.2