Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. We demonstrate how multidimensional stimulated Raman X-ray pulse sequences may be used to monitor the phase and dynamics of the nonequilibrium valence electronic state wavepacket created by photoexcitation or photoionization. Many important photophysical and photochemical molecular processes take place via conical intersections (COIS) where nuclear and electronic degrees of freedom become strongly coupled and the adiabatic Born Oppenheimer approximation beaks down. A new technique, TRUE-CARS, Transient Redistribution of Ultrafast Electronic Coherences in Attosecond Raman Signals, is proposed that can detect the passage through a COIS. X-ray pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn. Other applications include coherent control of long-range charge transfer in proteins and light harvesting complexes by resonant x-ray pulses.

Multidimensional spectroscopy of conical intersections by broadband x-ray pulses

253rd National Meeting (2017)

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