Irradiation of Ru(dmpe)2H2 (dmpe = (CH3)2PCH2CH2(CH3) 2) in cyclohexane solution with a picosecond pulsed laser at 300 nm leads to immediate formation of Ru(dmpe)2 and H2. The experiments show that metal-hydrogen bond cleavage, H-H bond formation, and rearrangement of the metal-phosphine skeleton occur within the instrument rise time of ca. 16 ps. A partial decay of the transient with a rate constant of 2.5 × 109 s-1 is also observed. The transient spectral data obtained for the short- and long-lived transients are similar. © 1994 American Chemical Society.