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Princeton Chemistry's Scholes Group is reporting evidence that quantum vibrations participate in electron transfer, establishing with ultrafast laser spectroscopy that the vibrations provide channels through which the reaction takes place.

Seeking to establish an experimental proof for a highly contested topic—the role of vibrations in processes fundamental to solar energy conversion—Princeton researchers set out to map the progress of a photoinduced electron transfer (ET) reaction.

The short laser pulses in ultrafast spectroscopy helped to lock all the light-absorbing entities in-step. Researchers were then able to watch the electron transfer dynamics and the vibrational dynamics simultaneously through beats created by the vibrational coherences. They found that the photoinduced ET reaction occurs in ~30-femtoseconds, which contrasts with conventional Marcus theory, and concluded that the unexpectedly rapid pace of the reaction revealed some unknown mechanisms at play.

"What we found is a unique cascade of quantum mechanical events occurring succinctly with the electron transfer reaction," said Shahnawaz Rafiq, a former postdoc in the Scholes Group and lead author of the paper. "These events appear sequentially in the form of loss of phase coherence along high-frequency vibrations, followed by impulsive appearance of a phase coherence along a low-frequency vibration.