Structural Kinetics by Stroboscopic Gas Electron-Diffraction .2. Time-Dependent Molecular Intensities of Predissociation Processes
by Ewbank, J. D.; Schafer, L.; Ischenko, A. A.
Various attempts have been reported in the literature [1-3] to develop stroboscopic gas electron diffraction (GED) for time-resolved studies of dynamic phenomena in laser-excited molecular species. This novel application of GED requires the formulation of new expressions for the scattering intensities, since conventional equations for GED data analysis are based on models that are restricted to equilibrium ensembles and molecules exhibiting small amplitude motions. As a first example, the time-dependent molecular intensities for species in adiabatic dissociative states have recently been reported [4]. In the current study the molecular intensity expression for the evolution of internuclear distances in predissociation processes on a diabatic potential energy surface is presented and some model radial distribution curves are shown. The structural kinetics of the photodissociation of NaI are modeled on a femtosecond time-scale. The time-dependent molecular intensities of NaI are directly parameterized in terms of the intramolecular potential energy surfaces and other parameters which characterize the transient state dynamics, as taken from experimental spectroscopic investigations reported in the literature. The acute dependence of the molecular intensities and radial distribution curves on the PES shows that solution of the inverse problem, i.e. determination of potential parameters from time-dependent electron diffraction data, is feasible in principle. As in the previous model study of adiabatic dissociative processes, it is found that details of the dynamics of photo-predissociation can be resolved on a time-scale shorter than that of the probing electron pulse. Furthermore, our analysis demonstrates the fundamental difference between the observables obtained from spectroscopy and electron diffraction: whereas no explicit structural information on the time-evolution of the nuclear configuration is obtained from spectroscopy, the molecular intensities of scattered electrons depend directly on the structural kinetics; i.e. the time-evolution of the internuclear distances.
- Journal
- Journal of Molecular Structure
- Volume
- 321
- Issue
- 3
- Year
- 1994
- Start Page
- 265-278
- URL
- https://dx.doi.org/10.1016/0022-2860(94)07995-1
- ISBN/ISSN
- 1872-8014; 0022-2860
- DOI
- 10.1016/0022-2860(94)07995-1