Rapid-flow resonance Raman spectra of the primary electron donor (a bacteriochlorophyll dimer known as P) and of the monomeric accessory bacteriochlorophylls (B) in the bacterial photosynthetic reaction center of Rb. sphaeroides have been obtained at 5 degrees C. The spectra were obtained using a shifted excitation Raman difference technique with excitation at 850 nm for the P spectrum and 800 nm for the B spectrum. Raman bands at 187, 204, 332, 564, 684, 730, 899, and 1163 cm(-1) are found in common in the P and B spectra, while unique modes appear in the low-frequency region of the special pair at 34, 71, 95, 128, and 484 cm(-1). The remaining strongly Raman-active monomer modes at 353, 385, 621, 761, 1010, 1114, and 1132 cm(-1) were not detected in the dimer spectrum. No substantial resonance Raman activity is observed above 1200 cm(-1) for either chromophore, indicating that high-frequency modes are not strongly coupled to the optical excitation in the Q(y) absorptions f of B or P. The Raman spectrum shows that the electronic excitation of P is coupled to at least 14 vibrational degrees of freedom, including low-frequency modes at 34, 71, 95, and 128 cm(-1). The Raman scattering cross sections for the modes of B are approximately an order of magnitude larger than those for analogous modes of P. This difference suggests that the excited electronic state of P is damped by rapid vibronic relaxation processes that are not present in B. The complete analysis of these resonance Raman results will lead to the development of specific multimode models for the excited-state structural dynamics and relaxation of the chromophores in reaction centers.