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Aqueous solutions of tetranitromethane (TNM), both deaerated and oxygenated, have been investigated by the technique of pulsed radiolysis. This system enabled the direct determination of ee6780, the extinction coefficient of the hydrated electron, at 5780 A. as 10,600 (±10%) Af-1 cm.-1. ee6780 is essential for evaluating rate constants previously determined as k/tam. Also from ee6780 we calculate Ge = 2.6 from values of Ge X ee67S0 in the literature. A number of rate constants were determined, including k(eaq~+ TNM) = 4.6 X 1010 Af-1 sec.-1, fc(H + TNM) = 5.5 X 108 Af-1 sec.-1, and k(eaq~+ NF-) = 3.0 X 1010 Af-1 sec.-1, where NFis the nitroform ion. Rate constants have also been measured for reaction of several organic radicals with TNM. In the presence of 02, k(02-+ TNM) was measured as 1.9 X 10® Af-1 sec.-1. fc(H02 + TNM) is less than 10-5 as large. Measurement of the effective k as a function of pH gave pK = 4.45 ± 0.25 for the dissociation, H02 H+ + 02-.(1) Based on work performed under the auspices of the U. S. Atomic Energy Commission.

The catalysis of methyl viologen radical cation (MV+•) decay reactions by gold sol, stabilized by either poly(vinyl sulfate) (PVS) or poly(vinyl alcohol) (PVA), was studied by pulse radiolysis. Stabilization of the sol by PVS eliminates the hydrogen evolution reaction as a pathway for MV+• decay. This is shown to be due to dimerization of MV"1"• (to the biradical) in the potential field of the polyelectrolyte. On PVA-stabilized sols, the hydrogen evolution reaction is a major pathway although side reactions (probably hydrogenation) interfere to a large extent. The rate of adsorption of MV+• on PVA-stabilized sol is controlled by the diffusion of MV"1"• to the gold particle. Subsequent reactions of protonation and electrochemical desorption, (Au)c""Hm + H30+ -*• (Au)c('1_1)"Hm_1 + H2 + H20, on a slower time scale are the rate-determining steps at the pH range and catalyst concentration used. At higher catalyst concentrations interparticle reaction is invoked to explain the dependence on [Au].(PVS) gold sol has been described previously.12 The other sol was stabilized by poly(vinyl alcohol) (PVA, Polysciences, Inc., 133 000 molecular weight). Approximately 100 mg of HAuC14 was dissolved in 500 mL of 0.1% PVA, and the pH adjusted with NaOH to ~11. CO gas was then bubbled through the solution for 10 min at room temperature. The resultant sol was then acidified with HC104 to pH 2.5 and then boiled for 1 h to expel CO or C02. The sol thus obtained had a spectrum similar to that of the Au/PVS sol previously described.12 Both sols were found

Aqueous solutions of Ru(bpy)32+ (bpy = 2,2,-bipyridine) were flash photolyzed and pulse irradiated in the presence and in the absence of other additives. Hydrated electrons are produced in a process which is suggested to involve electron ejection from the first triplet of Ru(bpy)32+, upon the absorption of a second photon. Most of the effective light (~70%) was in the range 300-340 nm, while ~30% of the effective light was at wavelength >340 nm. The efficiency of eaq~production relative to the efficiency of production of the lowest triplet charge transfer state was measured under our conditions as 0.0015, independent of [Ru(bpy)32+] and of flash intensity over a wide range. During our work on the biphotonic process for eaq" formation, a number of other reactions were investigated. Thus, hydrated electrons react with Ru(bpy)32+ with a reaction rate constant of (5.8 ± 0.3) X 1010 M"1 s"1. The metal ions Zn+, Co+, and Cd+ reduce Ru(bpy)32+ with reaction rate constants (1.5 ± 0.2) X 109, (1.7 ± 0.2) X 109, and (6.1 ± 0.6) X 108 M"1 s'1, respectively, producing Ru(bpy)3+. Ru(bpy)3+ reacts with 02, Cu2+, and duroquinone; the reaction rate constants are (7.2 ± 0.8) X 109, (3.4 ± 0.3) X 10s, and (4.0 ± 0.5) X 109 M"1 s"1, respectively. The possibility for a biphotonic effect leading to H2 formation is discussed.

systems should answer many of these questions in the near future. ConclusionsThe excitation-transfer rate constants of N2(A) to Cd are large with the favored channels being those with conservation of electron spin and large N,(A-X) FC factors. Our data suggest that Cd(3Po) and Cd(3P2) are important products, as well as Cd(3Pl). These results follow the same trends that were observed for N2(A) with Cu atoms,s and large excitation-transfer rate constants to metal atoms generally can be expected. Another way to express the Franck-Condon idea is to note that R(N2,A) in the entrance channel is larger than in the exit channel (for N,(X,v"=O), and favorable crossings with the entrance channel potential require stretching of N2(X) in the exit channel. The very large quenching rate constant suggests that strongly interactive exit channels cross the attractive entrance channel at long range. The intramultiplet mixing rates of Cd(3Po,2) with Cd(3Pl) are not rapid in Ar buffer gas. A weak Cd2* emission, tentatively associated with the Cd2( l~,~n,,) state, which could be formed by three-body recombination with Cd(3P2), was observed at high Ar and Cd concentrations. Qualitative observations of the CO(a311) + Cd reaction suggest a close similarity with the N2(A) reaction. Acknowledgment.The rates of the reaction of ethylene and ethylene-do with OH and OD were determined. The following reactions were examined: OH + C2H4 -products (HH); OD + C2H4 -products (DH); OH + C2D4 -products (HD); OD + C2D4 -products (DD). These reactions show different reaction pathways at different temperatures. Below 560 K there is a weak negative activation energy which is characteristic of the OH addition to the double bond. kHH and kHD were the same at 1.65 X 1O-I2 exp(480/T) cm3/(molecuIe s) while kDD and kDH were the same at 1.35 x exp(480/T) cm3/(molecule s). Above 720 K, all rate constants show a positive activation energy of 4-5 kcal/mol and both primary and secondary kinetic isotope effects were observed. The high-temperature pathway was attributed to the H abstraction from ethylene by the OH. A conventional transition-state-theory calculation (TST) successfully reproduced the temperature and isotope dependence of the H abstraction rate constants.

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Absolute rate constants for the gas-phase reaction of the OH radical with 1,3-butadiene and allene in an argon atmosphere were measured at 1 atm over the temperature range 305-1173 K. It was not possible to determine the rate of the H abstraction reaction from either allene or 1,3-butadiene; an upper limit for these rates is about twice that which one would predict from the OH + ethylene reaction. At temperatures below 600 K, k(OH + 1,3-butadiene) = (1.4 ± 0.1) X 10~" exp[(440 ± 40)jT\ cm3/(molecule-s) and k(OH + allene) = (6.7 ± 0.9) X 1CT12 exp[(100 ± 50)/7] cm3/(molecule-s). Above 600 K the rate constant of the allene reaction decreases weakly while the rate constant for the 1,3-butadiene reaction decreases markedly.