We found direct spectroscopic evidence for a reactive Co I intermediate in UV-Vis studies of our system. Irradiation of a solution containing [Co(dmgH)2pyCl], [Ru(bpy)3] 2+ , and BIH results in the rapid formation of two new absorption peaks at 530 and 656 nm in the UV-Vis spectrum (Figure ). These peaks have previously been assigned to the formation of a Co I intermediate. Upon either 1) purging this solution with C2H2 or 2) adding 1.0 M TFE, the