THEORY OF CONTINUUM MEDIATED 2-PHOTON IONIZATION, WITH APPLICATIONS TO CH3I

Theory of two-photon ionization via intermediate dissociative states i s developed. The theory is applied to the one-color two-photon ionizat ion of CH3I for which the (3)Q(0) and (1)Q(1) dissociative states serv e as intermediate resonances. Both CW and transient ionization spectra are calculated. The computed methyl iodide CW ionization line intensi ties are in profound disagreement with line intensities derived from t wo-photon zero kinetic energy electrons (ZEKE) experiments. The discre pancy may be viewed as evidence that ZEKE line-intensities are not sim ply proportional to the population of the ionic-core states. This extr a dependence on the ionic-core states, most likely due to the existenc e of external ions, can be accounted for by comparing our calculations to the observed ZEKE Line intensities. The dynamics revealed by ultra short pulsed two-photon ionization is also studied. In methyl iodide, we find that pulses capable of revealing ''real-time'' dissociative dy namics must be considerably shorter than 50 fs. (C) 1996 American Inst itute of Physics.