Nonadiabatic Reaction Dynamics of Polyatomic Molecules in the Proximity of the Conical Intersection
Abstract
Non-valence bound state (NBS) of the anion is ubiquitous in nature and plays the essential role of the doorway into the anion physics and chemistry. Here, the state-specific chemical dynamics of the metastable NBSs using the picosecond time-resolved pump-probe spectroscopy on the cryogenically cooled anions using the velocity-map ion/electron imaging technique has been utilized to unravel the nature of the mode-dependent dynamic behavior of the NBS in terms of the autodetachment and/or concomitant fragmentation reactions. The autodetachment rate of the NBS has been precisely measured in a state-specific way for various chemical systems of the phenoxide, 4-cyanophenoxide, or o- (m- or p-) halogen substituted phenoxides. Fermi’s golden rule is found to be extremely helpful for the rational explanation of the experiment, and yet the much more sophisticated theoretical model was required for the quantitative analysis. For (ortho-, meta-, or para-) iodophenoxides, the C-I bond rupture (giving the I- fragment at the asymptotic limit) has been found to be mediated by Feshbach resonances of the NBS, providing the foremost evidence for the dynamic doorway role of the NBS in the anion chemistry and physics.
Nonadiabatic dynamics at the conical intersection of the excited thioanisole has been interrogated by measuring picosecond time-resolved translational energy distributions of products, giving the evidence of distinct Herzberg type-I (electronic predissociation) or type-II (vibrational predissociation) channels. This gives deep insights into bifurcation dynamics in the vicinity of the conical intersection. Recently, the structural change of the methylamine (CH3ND2) near the transition-state has also been characterized by analyzing a large-amplitude vibrational progressions using IR+UV double resonances extended to the reaction barrier-top. Systematic flow of the vibrational energy into the reaction coordinate has unraveled strong coupling of the internal rotor to the N-D elongation coordinate.
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