A model for photodissociation dynamics applied to the potassium iodide system

Abstract

The objective of this investigation was to study the laser-induced photodissociation of potassium iodide in the vapor phase. The KI system was selected because of the high absorption cross-section and low enough bond energy to dissociate the molecule with the laser energy available (3.57 eV). A photofragment spectrometer was built in which a collision-free KI gas beam was crossed in a vacuum chamber by an intense, pulsed, polarized laser beam. Due to the directional nature of the polarized light and gas beams, the photofragments produced by the dissociation of the molecule are scattered in preferred directions. The intensity of scattered K atoms is measured as a function of laser light polarizer angle as referenced to a stationary surface ionization detector. Using a model developed for the purpose, the average symmetry and lifetime of the excited molecular state(s) is extracted from the intensity distribution. From the observed distribution characterized by a shift angle of 31 ± 8° and a shape factor of -0.14±0.04, it is concluded that dissociation occurs from at least two exited states of different symmetries with a mean lifetime of less than 0.01 picoseconds.