Direct observation of the coherent nuclear response after the absorption   of a photon
  How molecules convert light energy to perform a specific transformation is a fundamental question in photophysics. Ultrafast spectroscopy reveals the kinetics associated with electronic energy flow, but little is known about how absorbed photon energy drives nuclear or electronic motion. Here, we used ultrabroadband transient absorption spectroscopy to monitor coherent vibrational energy flow after photoexcitation of the retinal chromophore. In the proton pump bacteriorhodopsin we observed coherent activation of hydrogen wagging and backbone torsional modes that were replaced by unreactive coordinates in the solution environment, concomitant with a deactivation of the reactive relaxation pathway. 
Matz Liebel, Christoph Schnedermann, Giovanni Bassolino, Garrick   Taylor, Anthony Watts, Philipp Kukura
physics.chem-ph