Infrared multiphoton dissociation of styrene ions by low-power continuous CO2 laser irradiation

Abstract

The kinetics of infrared multiphoton dissociation of styrene ions under collision-free conditions in the ion cyclotron resonance ion trap were studied as a function of the intensity of the cw CO2 laser at powers up to 6 W. Following the beginning of irradiation an induction time was observed, followed by dissociation according to a first-order rate constant. The kinetics could be fitted to a random-walk simulation of a master-equation model, in the same way as previous studies. A matrix-algebra solution of the master-equation model is described which gave a better fit with greater computational convenience. From the modeling the rate of radiation of infrared photons (assumed to be at 940 cm−1) from the ions was estimated as 350 s−1 at an ion internal energy of around 3 eV. When the dissociation threshold Et was treated as an unknown it was found that master-equation modeling of the kinetic results could give an estimate of Et, but with large uncertainty. Application of simple thermal kinetic theory via Tolman’s theorem gave good qualitative understanding of the results, and predicted the intensity dependence of the dissociation rate with a deviation of about 30%.