Imaging Energy Flow and Predissociation Dynamics in Hydrogen-Bonded Complexes

Hydrogen bonding plays an important role in environments ranging from biological systems to ices in the solar system. While the structure of hydrogen bonded dimers is known for many systems, dynamical processes such as energy flow patterns and dissociation are much less known and hard to model theoretically. Photofragment imaging has been used to interrogate state-specific energy flow patterns and predissociation of hydrogen-bonded mixed dimers of polyatomic species. Imaging-based "dynamic spectroscopy" provides action spectra of photofragments following infrared excitation of selected vibrational transitions in the dimer. Pair-correlated energy distributions are inferred from velocity map images of specific product rovibronic states. Predissociation of dimers of acetylene with hydrogen halides and ammonia will be discussed, as well as the ammonia-water dimer. The experiments demonstrate that while general propensity rules can be formulated for energy redistribution and predissociation rates, it is the fine details of how excitation is deposited in the dimer and its subsequent propagation through the two dimer moieties that give rise to pronounced state-specific effects. Calculations based on the hard-ellipsoid model illustrate how kinematic constraints can determine points of impact and the ensuing transformation of linear to angular momentum.

For more information contact Prof. Christine Payne (404-385-3126).