Oscillations within the BL absorption band of Rhodobacter sphaeroides reaction centers upon 30 femtosecond excitation at 865 nm

Sub-picosecond oscillations in the BL band were found in native and BM-modified reaction centers of Rhodobacter sphaeroides R26 at 293 K using 30 fs excitation pulses at 865 nm. The Δ A spectrum, polarization measurements and frequencies of the kinetic oscillations are consistent with the notion that these oscillations are due to the wavepacket nuclear motions associated with electron transfer from the excited primary donor P∗ to BL at the intersection of the reactant (P∗ BL) and product (P+ BL−) potential energy surfaces. The time-position of the wavepacket at the intersection corresponds to the minimal and to the maximal P∗ stimulated emission at the short-wavelength and at the long-wave sides of the emission band, respectively. A protein vibration mode of 30 cm−1 is likely to play an important role in the electron transfer.