Seminar of the School of Physical Sciences
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Title: Spectroscopy and Dynamics of Hydrogen Bonded Networks: Imaging Bond Breaking Pathways
Speaker: Amit Kumar Samanta
(University of Southern California, Los Angeles)
Date: March 9, 2016 (Wednesday)
Abstract: The hydrogen bond (H-bond) is the most pervasive and important noncovalent bond in nature. For nearly a century theoreticians and experimentalists have tried to understand all aspects of H- bonding and its influence on reactivity. It is somewhat surprising, therefore, that several fundamental aspects of H-bonding that are particularly important for benchmarking theoretical models have remained unexplored experimentally. For example, even the binding strength between two gas-phase water molecules has never been determined with sufficient accuracy for comparison with high-level electronic structure calculations. Likewise, the effect of cooperativity (nonadditivity) in small H-bonded networks is not known with sufficient accuracy. An even greater challenge for both theory and experiment is the description of the dissociation dynamics of H-bonded small clusters upon acquiring vibrational excitation. I will present a brief overview of the newly developed application of velocity map imaging (VMI) to study state-to-state vibrational predissociation dynamics of H-bonded clusters following vibrational excitation. Combination of VMI and resonance enhanced multiphoton excitation (REMPI), allowed us to determine bond dissociation energies of small dimers and cyclic trimers of water and HCl with unprecedented accuracy, describe dissociation dynamics, and assess the effects of cooperativity. Our success with water and HCl dimers and trimers led us to embark on a more ambitious project: studies of mixed water and HCl small clusters. These clusters eventually lead to ionization of HCl and serve as prototypes of acid dissociation in water. The details will be discussed during the presentation.
