Mh. Vos et al., COHERENT NUCLEAR-DYNAMICS AT ROOM-TEMPERATURE IN BACTERIAL REACTION CENTERS, Proceedings of the National Academy of Sciences of the United Statesof America, 91(26), 1994, pp. 12701-12705
A room-temperature study is reported of the femtosecond spectral evolu
tion of the stimulated emission band of the primary electron-transfer
precursor P in bacterial photosynthesis. The study was performed with
membranes of the antenna-deficient RCO1 mutant of Rhodobacter sphaero
ides. A time-dependent red shift, reflecting nuclear motion out of the
Franck-Condon region of the excited state, is resolved. Analysis of o
scillatory features persisting for >1 ps in the kinetics revealed main
frequencies of the activated motions at 30, 84, 145, and 192 cm(-1).
The oscillations occur on the time scale of primary electron transfer.
Our results set a lower limit for the vibrational dephasing time in P
that is not compatible with the usual assumption in theoretical trea
tments of complete vibrational relaxation prior to electron transfer,
even at room temperature.