STRUCTURAL KINETICS BY STROBOSCOPIC GAS ELECTRON-DIFFRACTION .1. TIME-DEPENDENT MOLECULAR INTENSITIES OF DISSOCIATIVE STATES

Theoretical analyses and model calculations are presented for the appl ication of stroboscopic gas electron diffraction as a technique to stu dy the structural kinetics of transient species in the femtosecond tim e domain. An expression for the time-dependent molecular diffraction i ntensities is developed and used to model the dynamics of the laser-in duced dissociations of IBr and ICN. It is found that the molecular int ensities can be directly expressed in terms of the potential function of the dissociative state and other parameters that characterize the t ransient state dynamics. Thus, the solution of the inverse structural problem seems feasible, i.e. the determination of transient state para meters from time-dependent intensity data. In addition it is found tha t structural details of the dissociative processes can be time-resolve d on a scale that is significantly faster than that of the electron pr obe pulse width. Our study indicates that, by measuring directly the e volution of transient state geometries, time-resolved electron diffrac tion provides a new type of information complementary to that obtained by spectroscopic techniques.