| Time-resolved Pump–Probe Spectroscopy to Follow Valence Electronic Motion in Molecules: Theory and Simulation | |
| Presenter | Anthony Dutoi, University of the Pacific |
| Session Title | Capturing the Dynamics of Electrons in the Time Domain |
| Abstract | Anticipating the experimental realization of attosecond pulses with photon energies up to 1 keV, we have developed a formalism that connects the evolution of a nonstationary electronic state to an X-ray probe signal. The electronic states we propose to follow evolve on the femtosecond time scale, and their valence occupancy structure can be probed in both space and time by taking advantage of the inherent locality of core–valence transitions, the comparatively short time scale on which they can be produced, and the ability to distinguish atoms by their widely separated core–valence energy gaps.
Our formalism makes use of the time-dependent one-electron reduced density operator, which is a compact representation of the character of an arbitrary electronic state. This allows for a connection to be made between the complexity of the many-body wavefunction that underlies reality and advanced simulations and an intuitive picture of dynamic orbital occupancy. We show that one-electron information (from an accurate wavefunction) is the dominant contribution to the attosecond transient absorption signal, on account of the broad pulse band width involved. Numerical experiments have been performed using an all-electron model, computing dynamics after a localized excitation on a model chromophore group. The choices of functional groups in the molecules investigated were loosely motivated by a debate over the character of a proposed electron transfer in much slower amino-acid photofragmentation studies, themselves relevant to a larger discussion about photodamage in organisms. Our congruous results potentially illustrate the robustness of the principles that control electronic dynamics across largely varied time scales. |