7539
gonne National Laboratory's A R C 0 linear accelerator, in accord with the general procedures described elsewhere. Experimental conditions were maintained so as to ensure the rapid (t1l2 0.1 psec) scavenging of OH radicals, either by'methanol (-lo-, M ) in the case of the C O ( C N ) ~ ~solutions, or by Hz (-0.1 M , achieved by using a high-pressure cell4 containing 100 atm of H2) in the case of the other solutions. The pH, in each case, was maintained at 13; under these conditions H atoms were rapidly (t1l2 0.35 psec) converted by OHto e,, so that, for our purposes, e,, was effectively the only reactive species generated by the pulse radiolysis. The reactions of the hydrated electrons with the cobalt complexes were monitored spectrophotometrically as previously described, the spectra of transient species being deduced from the absorbance changes accompanying their formation and/or decay. The overall stoichiometries of the reactions were confirmed in steady-state irradiation experiments using a V o y source. Pulse radiolysis experifnents on aqueous solutions of Co(CN)j3M ) , in which the generation and decay of e,, were followed at 578 nm (E 1.1 X lo4 M-' cm-l), revealed a reaction between e,, and Co(CN)j3- which obeyed the second-order rate law, k l [e,q-][Co(CN)53-], with kl = (1.4 f 0.1) X 1Olo M-l sec-'. The initial product of this reaction is a transient, 280 identified below as pentacyanocobaltate(1) (A, nm, E,, -8 X lo3),which undergoes first-order decay (k, = (1.0 f 0.1) X lo5 sec-l) to yield C O ( C N ) ~ H ~ - . In D 2 0 solutions the value of kl was substantially the same as in HzO, whereas the value of kz was reduced to 1.6 X lo4 sec-', one-sixth its value in H 2 0 . We interpret these observations in terms of the following reaction sequence.
-
-
+
ki
CO(CN)~~- ea,-
+
+CO(CN)~'-
k2
+
(1)
C O ( C N ) ~ ~ - H20 +Co(CN)5H3- OHC O ( C N ) ~ ~ -HzO cap- +CO(CN)~H~- OH-
+
+
+
(2)
nm, E -lo3), which decayed with half-lives of -10-8 and 10-6 sec, respectively, in accord with the pattern depicted by eq 3 and 4, to yield C O ( C N ) ~ ~(-50%) and CO(CN)~& (-5OX), respectively. Co(CN)?
