Excitation-wavelength dependence of the transient absorbance changes of photosystem I reaction center particles with a reduced number of antenna chlorophylls (16 chlorophylls/primary electron donor chlorophyll (P700)) has been studied in an effort to understand the energy equilibration among the chlorophylls in the electron-transfer system. The photobleaching and stimulated-emission signals in the Q, band region of the chlorophylls upon the preferential excitation of chlorophyll spectral forms at the blue edge (662 nm) and red edge (697 nm) of the Q, band are analyzed. In the case of the red-edge excitation, spectral equilibration proceeds with a time constant of 0.34 (+/-0.07) ps, which is attributable to the energy equilibration between P700 and neighboring chlorophylls absorbing around 686 nm in the electron-transfer system. This equilibration seems to precede the fastest phase of the primary charge separation (apparent time constant of 0.8 ps) reported previously (Kumazaki et al. J. Phys. Chem. B 2001, 105, 1093). A slow decay of the excited states because of the slow phase of the primary charge separation proceeds with a time constant of 7.2 (+/-0.6) ps. In the case of the blue-edge excitation, vibrational relaxation and downhill energy transfer proceed with a time constant of 0.38 (+/-0.08) ps, which are followed by a slow downhill energy transfer from residual antenna chlorophylls to the electron-transfer system. Even with the slow energy transfer from the residual antenna chlorophylls to the electron-transfer system, the overall primary charge separation is completed with a time constant of 10 (+/-0.7) ps. These interpretations are in part supported by control experiments on chlorophyll a in ethanol under equivalent optical conditions. Implications of these results for understanding the primary processes in more intact photosystem I are discussed.