The primary, light-induced charge separation in reaction centers of Rhodopseudomonas widis is investigated with femtosecond time resolution. The absorption changes after direct excitation of the primary donor P at 955 nm are investigated in the time range from 100 fs to 600 ps. The experimental data, taken at various probing wavelengths, reveal one subpicosecond and two picosecond time constants: 0.65 k 0.2 ps, 3.5 k 0.4 ps, and 200f 20 ps. The previously undetected 0.65 ps kinetics can be observed clearly in the spectral range of the QX and Qu transitions of the monomeric bacteriochlorophylls. The experimental data support the idea that the accessory bacteriochlorophyll B, participates in the electron-transfer process.

The spectral properties of the excited electronic state of the reaction centers of Rhodopseudomonas (Rps. ) viridis are studied by dichroic transient absorption spectroscopy with sub-picosecond time resolution. The theoretical analysis of the experimental results allows the assignment of the transient absorption from two dimer bands of the special pair and show its excitonic coupling to other pigments.

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