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We show that there are several compounds whose ability to decrease the initial 50-ps yield of the hydrated electron is not correlated with the reactivity of that compound. Several mechanisms have been proposed. Explicit corrections have been included for time-dependent reaction rates. It is shown that other corrections require assumptions about the mechanism of the presolvation reaction.

Publication costs assisted by Argonne National LaboratoryEnergy is deposited by fast electrons in water in small localized volumes called spurs. The decay of the hydrated electron in a spur has been measured to be about 17% between 100 ps and 3 ns. Half of this decay occurs before 700 ps where previous techniques could not observe any decay. The principal reactions of the hydrated electron in the spur are presumed to be eaq-+ eaq~, eaq-+ H+, and eaq-+ OH. Scavengers for the hydrogen ion are about equally effective in slowing the decay as are scavengers for the hydroxyl radical except for OHwhich seems unusually effective. This suggests H+ and OH are distributed similarly with respect to eaq". Spur decay is also observed for the products of electron capture, Cd+ or RSSR-, where RSSR is cystamine. The observations reconcile different methods for measurement of the initial hydrated electron yield to 4.6 ± 0.2 molecules/100 eV, and combined with our earlier data, provide the major features of the history of eaq-in the spur from 100 ps to the achievement of a homogeneous distribution.

The flash photolvsis of aqueous solutions of iodide, bromide or chloride ions produces unstahle species believed to be the dihalide ions. The maximum of the longest wave length and most prominent band is at 370 mp for iodide ion, 350 mp for bromide ion and near 340 mp for chloride ion. The assignment is supported by experiments showing that the flash irradintion of triiodide ion in the 353 mp absorption band produces a transient species whose spectrum nnd decay kinetics closely resemble those obtained from iodide ion. Assuming the common identity of the transient species, the maximiini extinction coefficient of diiodide ion is estimated as 15,6000 f 3000 Ad-1 cm.--1. Flash spectrophotometry a t 404.7 mp shows that diiodide ion from air-free KI solutions disappears by a pH independent, second-order process whose rate increases with decreasing iodide ion concentration. The data are consistent with the establishment of the equilibrium: (1) I + I-* 12-, and the disappearance of diiodide ion by any of three bimolecular reactions: (2) 21 + 1 2 ; (3) I + 12--.t 11-; and (4) 212-+ Is-+ I-, the relative importance of each depending upon the iodide ion concentration. Analysis of the results gives 7.7 f 1.5 X lOg M-1 sec-1 for the rate constant of reaction 4 and a minimum value of 1.2 X lO4for K,. The rate constants for the disappearance of diiodide ion produced by flash irradiation of iodide ion or triiodide ion agree to within 157, a t high iodidc ion concentrations.

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FAHADAY. cordon. h »m, maim i o n . k aaa ni ?mamas' i A T F M>K R FADING. SFF1FM BIR W O O F . S U W IC T TO ftC V tttO N ««r F1.d w 4 eedrem # mere formed in the electron t'utse »# t wfsaied w tu tw m a: cwKW tn tw w i m the range from I to jyi mM »>e»r reaction was foM.>we%< by the decs; of the optical absorpthwi of em at 5780 A (ieneraUv a 0 4 pace pulse of 15 McV electron?, was used In ih* absence of *>«, scavengers, ucond-order kinetics prevailed oss mg to the domm anec *sf the reactions, r , scavengers were present in alkaline volution «if 0*t I©1" and i i *■*". ein, H, and *^4 H.^O? when OH radical An analysts of the tk.'as curves leads to value* for an *m -«* * H o f H ICM " and I -!©!U M 1 sec *, T e iw in m With scavenger presen, tn excess over fr^l pseudo first-order kinetic* were found and rate constants for a number of t not gam*, and organ*. compounds are reported The agreement o ' these and other rate constants with dvfftifuon-controHed reaction theory t» discussed *

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.

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