Using ultrafast laser spectroscopy, the study authors found that quantum vibrations provide transfer channels.
American chemists from Princeton University have collected new evidence that quantum vibrations play an important role in the transfer (transfer) of electrons. An article about this work, published in Nature Chemistry, may turn out to be an important milestone in the study of solar energy conversion processes.
Using ultrafast laser spectroscopy, the study authors found that quantum vibrations provide channels for particle transport. The main task that the scientists faced during the experiment were to isolate from the huge number of vibrational coherences (mutual consistencies of vibrational processes) generated by laser radiation, directly related to electrons’ transfer. Short laser pulses in ultrafast spectroscopy helped to synchronously block all light-absorbing objects, allowing researchers to study the transfer process without interference.
Chemists have found that the transfer reaction lasts about 30 femtoseconds, which is in sharp contrast to the current generally accepted Marcus theory (description of the process of electron transfer in a polar solvent in the framework of semiclassical approximations). “We have discovered a unique cascade of quantum mechanical events that occur in an electron transfer reaction within a minimal time frame,” said lead author Shahnavaz Rafik.
The events that Rafik talks about manifest themselves as a loss of phase coherence along with high-frequency vibrations, followed by a pulsed appearance of phase coherence along with the high-frequency vibrations. The authors also found that the electron transfer reaction product has an additional wave packet (a certain set of wave characteristics in limited space and time), which the reactants do not have. From this, scientists conclude that the vibrational modes’ frequencies determine the order of structural changes in the molecules involved in the reaction.
“It is generally accepted that a wave packet can only be generated using a photon pulse,” explains study co-author Bo Fu. “But here we saw a wave packet that does not seem to be generated by such an impulse. Simulation of quantum dynamics helped us to establish that this wave packet, in fact, was created by the electron transfer reaction”.
Chemists have compared the generation of wave packets during electron transfer with stretching a vibrating spring to a more stable position. The spring vibrates with significantly greater amplitude relative to its new mean position. This response of synchronized vibrations of the molecular structure provides a mechanism for inhibiting the particle transfer’s coherent repetition.