Uv-laser photofragmentation instrument: Multiphoton ionization and dissociation of small molecules

Abstract

An excimer laser-based photofragmentation instrument capable of quantitatively probing ionization and dissociation dynamics in small molecular systems is described. This instrument combines single and multiphoton excitation techniques, with fluorescence and time-of-flight ion detection techniques to excite specific excited states of parent molecules and to determine the partitioning of energy among neutral and ionic photofragments. The results of a series of prototype photofragmentation experiments on CO will be used to demonstrate how the experimenter obtains a clearer picture of the fragmentation mechanism when both the ionic and neutral photofragments are interrogated quantitatively rather than when only one type of fragment is studied. Specifically, the authors address the discrepancy in the interpretations of previous fluorescence work on the CO system. It will be shown further that the spectra of the photofragments generated after decomposition of CO by 193-nm radiation can be used to calibrate the laser bandwidth (0.75 cm−1) and the absolute frequency (to within 2 cm−1) when an ArF* excimer laser is employed.