Molecular photofragmentation with many infrared photons. Absolute rate parameters from quantum dynamics, statistical mechanics, and direct measurement

Abstract

The quantum-dynamical and statistical mechanical foundations of the definition and determination of absolute rate parameters for molecular photofragmentation with infrared lasers are discussed briefly and are illustrated with model calculations. A new experiment is reported, which allows the measurement of iodine atom yield in real time as a function of fluence during the laser pulse for the fragmentation of perfluoroalkyl iodides C_nF_2n+1I (n= 1–10). The data are evaluated quantitatively in terms of the absolute rate coefficients. The results are compared to results from indirect measurements and to theoretical calculations. The importance of the transition from non-linear case C behaviour to linear case B behaviour is demonstrated for CF₃I in the experimentally accessible intensity range. The transition falls in the intensity range predicted quantitatively from a simple theoretical model.