IMPULSIVE EXCITATION OF COHERENT VIBRATIONAL MOTION GROUND SURFACE DYNAMICS INDUCED BY INTENSE SHORT PULSES

A framework for understanding impulsively photoinduced vibrational coh erent motion on the ground electronic surface is presented. In particu lar strong resonant excitation to a directly dissociative electronic s urface is considered. Three distinct approaches are employed. A two su rface Fourier wavepacket method explicitly including the field explore s this process in isolated molecules. A coordinate dependent two-level system is employed to develop a novel analytical approximation to the photoinduced quantum dynamics. The negligible computational requireme nts make it a powerful interactive tool for reconstructing the impulsi ve photoexcitation stage. Its analytical nature provides closed form e xpressions for the photoinduced changes in the material. Finally the f ull simulation of the process including the solvent effects is carried out by a numerical propagation of the density operator. In all three techniques the excitation field is treated to all orders, allowing an analysis of current experiments using strong fields, resulting in subs tantial photoconversion. The emerging picture is that the impulsive ex citation carves a coherent dynamical ''hole'' out of the ground surfac e density. A rigorous definition of the dynamical ''hole'' is construc ted and used to define a measure of its coherence. In particular all p hotoinduced time dependence in the system can be directly related to t he dynamical ''hole.'' All, three techniques are used to simulate the pump probe experiment on the symmetric stretch mode of Gamma(3), inclu ding electronic and vibrational dephasing.