The transient absorption produced by the pulse radiolysis of CNS-is shown to be due to (CNS)z formed by the reactions : 1 OH+CNS-+OH-f CNS, CNS + CNS-+ (CNS) .;The rate constants of reactions (l), (2) and (3) at 22°C determined from kinetic and equilibrium measurements are 2-8 x lolo, 7.0 x lo9 M-l sec-l and 3.4 x lo4 sec-l, respectively. For iodide ion, which forms I2 in the same way, the equilibrium constant for Iz formation is 1.13 x lo5 M-l.The corresponding kinetic constants cannot be determined as accurately as for CNS-but are estimated to be 3-4 x lolo, 7.6 x lo9 M-' sec-l and 6 x lo4 sec-'. 2 3Previous pulse radiolysis and flash photolysis studies 1-4 on the halide ions have shown that, following the production of the halogen atom by oxidation or photolysis, the diatomic ion is formed, e.g., HzO-+H, OH, e; Y I-+ OH+I + OH-I + 1-4,. EXPERIMENTALThiocyanate and iodide were used as the potassium salts. Solutions of pH 2 and 7 were made with perchloric acid and a phosphate buffer respectively. These materials were of analytical reagent grade and solutions were made up in triply-distilled water.The pulse radiolysis apparatus has been de~cribed.~ In the present work the necessary low doses and consequent low absorptions required the use of a long light path reaction cell.An internal reflection cell ' was used which has an effective length of 64 cm at 475 nm, the wavelength convenient for observing the thiocyanate transient absorption, and about 30 cm at 365 nm used for the iodide system. At these low doses (6-30 rad/pulse) and absorptions, 2389 Pulse radiolysis and flash photolysis of I-have established that the transient species with A , , , = 380 nm is the 1, ion formed by I+I+I, K ,As with (CNS); the value of K2 can be obtained using the equation,where D is the optical density due to I; at various concentrations of I-. Plots of this equation are given in fig. 6 and the values of K , in various conditions are collected

A specimen chamber is described for soft X-ray spectromicroscopy of hydrated specimens and solutions. Applications include imaging and carbon edge spectroscopy of hydrated clay/polymer suspensions.

THE transient univalent states of certain metals, e.g., Znf, Ni+, Pbf, Cdf, Co+, can be produced in aqueous solution by reduction of the corresponding M2+ ions with hydrated These species absorb in the U.V. and their reoxidation can be followed using pulse r a d i ~l y s i s . ~, ~ We have examined their reactions with some oxidants including the M2+ ions, e.g.

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The relative rate constants for the reactions of hydrogen atoms with Fe(II), Cu(T1) and methanol, have been obtained over a range of pH. Fe(I1I) reacts entirely as Fe(OH)2+ and there is no measurable contribution from Fe3+ even in 0.2N perchloric acid. The ratio of rate constants are: MeOH : FeOH2+ : CuZf : : 1 : 480 : 38, and kFeOH2 +9500 k ~~3 +.