[Phys-seminars] 2017-01-19 Lasers Seminar
barmash at bgu.ac.il
Sun Jan 15 12:52:07 IST 2017
PLACE: Physics building (#54) room 207
Can internal conversion be controlled by mode-specific vibrational excitation in polyatomic molecules?
Michael Epshtein, Department of Physics, Ben-Gurion University of the Negev
Non-adiabatic dynamics at conical intersections (CI) extensively affects the photostability of biomolecules by efficiently photoinducing decay routes that dissipate harmful excess ultraviolet energy. Since one of the means for controlling the course of dissociation is considered to be selective excitation of vibrational modes containing a considerable component of motion, we have chosen to study here the predissociation of the model test molecules, methylamine (CH3NH2) and its deuterated isotopologues, excited to different specific vibrational modes in the electronically excited state. The first demonstrated detection of H(D) photofragments by Doppler-free (DF) ion imaging and velocity-resolved action spectra allowed measurement of the entire velocity distributions of the photofragments in each laser pulse and getting insight into the dynamics. The \"fast\" and \"slow\" H(D) products, resulting from N-H and N-D bond cleavage, obtained via two different dissociation pathways,
showed anomalous distributions for some rovibronic states, as indicated by dynamic resonances in the product branching ratio, in the internal energies of the CH3NH(D) photofragments and in the anisotropy parameters of the fast H photofragments. These correlated anomalies for predissociation initiated from specific rovibronic states allowed to reach energetic regions on the excited electronic states that led to dynamic predesign and control of the ensuing photoproducts, and are not necessarily related to the distinctive pre-excited nuclear motions. These resonances play an important role in the bifurcation dynamics at the CIs in the different isotopologues and can be foreseen to exist in other photoinitiated processes and to control their outcome.
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