The Interplay of Vibrational Coherence and Photoinduced Ultrafast Chemical Reactions

In ultrafast photoinduced chemical reactions, intramolecular vibrations can serve as sensitive probes of the underlying reaction dynamics in time-resolved pump-probe spectroscopy. Vibrational coherence is initially created by broadband pulsed excitation. The subsequent ultrafast chemical reaction can enhance, suppress, or even create new coherent nuclear wavepackets, owing to the sudden change in nuclear parameters in the product: a quantum quench effect. Using numerically exact quantum dynamics, we show that quantum quench effects significantly impact the final vibrational coherence observed in ultrafast excited-state proton and electron transfer reactions. We find that the multidimensional quantum dynamics provide microscopic insights to prior experimental observations, such as selective suppression or amplification of coherent vibrational spectra (CVS) peak intensities, phase shifts, and damped oscillations of vibrational beats. The quantum quench formalism provides a new framework for interpreting the transient spectroscopic features to obtain critical information on reaction coordinates from the multidimensional vibrational space.