Mapping photoisomerization dynamics on a three-state model potential energy surface in bacteriorhodopsin using femtosecond stimulated Raman spectroscopy.

The process of proton translocation in , triggered by light, is powered by the photoisomerization of all--retinal in bacteriorhodopsin (bR). The primary events in bR involving rapid structural changes upon light absorption occur within subpicoseconds to picoseconds. While the three-state model has received extensive support in describing the primary events between the H and K states, precise characterization of each excited state in the three-state model during photoisomerization remains elusive.