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October 15, 2014

Speaker: Michael Schuurman, National Research Council of Canada

Title: Simulating Photoinitiated Molecular Dynamics with Ab Initio Quantum Chemistry

Abstract: The absorption of a photon of light by a molecule is the first step in a process that can yield numerous competing dynamical relaxation pathways that ultimately result in disparate chemical outcomes that include radiative decay (flourescence, phosphoresence), nonradiative decay (internal conversion), or fragmentation. Constructing a microscopic understanding these processes has immediate and obvious implications on a wide swath of photochemical problems, including artificial light harvesting and mechanisms of photodamage on the DNA of biological systems. In this talk I will present techniques by which the excited electronic state dynamics of molecular systems can be interrogated on the natural femtosecond timescales of vibrational motion. In particular, I will focus computational and theoretical approaches for simulating these processes, which invariably involve nonadiabatic transitions between electronic states and are often mediated by the presence of conical intersections. The relationship between experimental results and computational simulation, and the best methods to compare the two, will be explored in detail. Time-resolved photoelectron spectroscopy will be shown to be a particularly sensitive probe of the type of dynamics (i.e., vibronic) of interest and it will be shown that the direct simulation of these experimental observables using ab initio approaches is the most unambiguous, and thus preferred, manner in which theory can complement complex time-resolved experimental measeurements.