LASER-INDUCED PHOTOFRAGMENTATION OF TRIETHYLALUMINUM - MODELING H-ATOM PRODUCTION

A rate-equation approach is presented that models H-atom formation during the pulsed laser photolysis of a triethyl metal compound, the specific case being triethylaluminum excited at 193 nm. An excimer laser initiates the chemistry under collisionless conditions, and H atoms are produced that are detected using two-photon ( 121.6 + 364.7 nm) ionization. Experimentally, the H-atom intensity is monitored as a function of photolysis laser power. Mechanistically, the primary photodissociation step is postulated to involve cleavage of the metal-carbon bond, thereby producing an ethyl radical. This species can then either: ( 1 ) form C2H4 and H directly; or (2) absorb an additional photon and produce an H-atom photofragment. The rate equations and their solutions allow one to calculate how H-atom production should vary as a function of photolysis laser power, and the interplay between the two H-atom production channels is calculated for various absorption cross sections and dissociation rates. A comparison with experimental power dependence data suggests that an overall one-photon dissociation process predominates under the experimental conditions actually used. © 1990 American Institute of Physics.