Simulating Transient Absorption Spectra using Extremely Broad X-ray Pulses

Document Type




Conference Title

American Chemical Society Meeting


American Chemical Society (ACS)


San Francisco, CA

Conference Dates

August 10-14, 2014

Date of Presentation



Extremely short (less than 1 fs) soft x-ray pulses are emerging as cutting-edge tools for investigating molecules on time scales shorter than the oscillation of a chemical bond. The very large photon energies and band widths of such pulses pose serious challenges for ab initio simulations of transient x-ray absorption spectra because the relevant final molecular states are so high in energy (and are generally decaying), and because so many states will participate. We build a theoretical framework, within which electronically correlated computations can be used to understand the x-ray absorption spectra of vibrating molecules, resolved both spectrally and in time. In particular, absorption at core–valence resonances are computed as a function of the stretch coordinate for halogen molecules and their molecular ions. This yields insight into what spectral features can be expected when an x-ray probe is used to follow vibrational dynamics in real time. In experiments with Br2, strong-field ionization has already been seen to produce coherent stretching oscillations of both the molecular ion and the depleted neutral species. Foremostly, detailed understanding of the dominant transitions that contribute to such a spectrum is desired (their character, intensity, line shape, and dependence on the vibrational coordinate). This study lays the foundation for eventual convergence of combined experimental and theoretical study of a common system.

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