Temperature Dependence of the Q<sub>y</sub> Resonance Raman Spectra of Bacteriochlorophylls, the Primary Electron Donor, and Bacteriopheophytins in the Bacterial Photosynthetic Reaction Center<sup>†</sup> CherepyNerine J. ShreveAndrew P. J. MooreLaura BoxerSteven G. MathiesRichard A. 1997 Q<sub>y</sub>-excited resonance Raman spectra of the accessory bacteriochlorophylls (B), the bacteriopheophytins (H), and the primary electron donor (P) in the bacterial photosynthetic reaction center (RC) of <i>Rhodobacter sphaeroides</i> have been obtained at 95 and 278 K. Frequency and intensity differences are observed in the low-frequency region of the P vibrational spectrum when the sample is cooled from 278 to 95 K. The B and H spectra exhibit minimal changes of frequencies and relative intensities as a function of temperature. The mode patterns in the Raman spectra of B and H differ very little from Raman spectra of the chromophores <i>in vitro</i>. The Raman scattering cross sections of B and H are 6−7 times larger than those for analogous modes of P at 278 K. The cross sections of B and of H are 3−4 times larger at 95 K than at 278 K, while the cross sections of P are approximately constant with temperature. The temperature dependence of the Raman cross sections for B and H suggests that pure dephasing arising from coupling to low-frequency solvent/protein modes is important in the damping of their excited states. The weak Raman cross sections of the special pair suggest that the excited state of P is damped by very rapid (<30 fs) electronic relaxation processes. These resonance Raman spectra provide information for developing multimode vibronic models of the excited-state structure and dynamics of the chromophores in the RC.