Excited State Dynamics

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This program employs computational quantum chemical methods to reveal not only how molecules respond on femtosecond timescales to the absorption of a photon of light, but also how this dynamical response may be observed using time-resolved spectroscopic techniques.  Our approach utilizes trajectory simulations in which the time-evolution of the atomic and electronic degrees of freedom of molecules are determined by computing potential energy surfaces 'on-the-fly' using ab initio electronic structure methods.  However, molecular trajectories are not observable quantities; this requires that the molecular wave packet be probed using ultrafast laser pulses.  The ability of high-level simulation to predict the resulting time-resolved spectra unifies theoretical and experiment approaches to unravel the mechanistic details of ultrafast phenomena.  Our group is engaged with a wide network of experimental collaborators, in both academic ultrafast laser labs and advanced light source facilities, to investigate novel methods of interrogating molecular motions on inherent timescales.***The current proposal will employ a total of four NSERC supported students in three main research thrusts: 1) the development of model theories for molecular excited state dynamics, 2) the 'complete simulation' of time-resolved spectroscopic experiments, and 3) investigation of the potential for novel X-ray probes of molecular dynamics.  The first research thrust addresses a persistent gap in our understanding of excited state processes: the lack of descriptive theories and models for excited state processes.  The ultimate goal of running our "simulation machinery" on specifically chosen molecular examples and model systems is the construction of rules governing dynamics involving (conically) intersecting electronic surfaces. The second thrust recognizes that validation of dynamical methods require comparison to experimental results. The most unambiguous comparison to be made is via the direct simulation of experimental observables. Our group is uniquely positioned, both in the simulation toolkit we've developed and in the network of experimental collaborators we employ, to demonstrate the ability of theoretical methods to speak to modern ultrafast experiments.  Lastly, developments in light sources now allow for femtosecond X-ray pulses that may be deployed in ultrafast pump-probe experiments. The wavelengths of X-ray photons is on the order of interatomic distances and promise to yield location specific information on the electronic environment at particular atomic sites in a molecule.  Our aim is to guide the interpretation of these new experiments using our well-positioned techniques. This program will provide students with an opportunity to conduct leading-edge, multidisciplenary research within a global network of theoretical and experimental collaborators.**