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The radiation chemistry of aqueous benzene solutions has been studied by the electron-pulse radiolysis technique. Ultraviolet absorption spectra of some of the transient species have been recorded by synchronized flash-absorption spectroscopy. The elementary reactions occurring have been observed by fast photoelectric recording of the transient optical density. A transient spectrum having a broad absorption with a strong maximum at 313 mμ has been observed. On the basis of both spectrographic and kinetic evidence this spectrum is assigned to the hydroxycyclohexadienyl radical, (OH)C6H6·. The molar extinction coefficient is estimated to be ε3130=3500±800 M—1cm—1. A number of substituted cyclohexadienyl radicals have been observed in aqueous solution as well as in pure benzene and chloro-benzene. A second transient observed in oxygenated aqueous benzene solution shows an absorption shifted to lower wavelengths. This is attributed to the hydroxycyclohexadienyl peroxy radical, (OH)C6H6O2·. Absolute rate constants have been determined at 23°C for the following reactions: OH+C6H6=(OH)C6H6·(4.3±0.9)×109 M−1sec−1,OH+C6D6=(OH)C6D6·(4.7±0.9)×109 M−1sec−1,(OH)C6H6·+O2=(OH)C6H6O2·(5.0±0.6)×108 M−1sec−1. The yield of phenol in oxygenated solution was found to decrease continuously with increasing pulse intensity. At the highest intensity used, G(C6H5OH) = 0.19 molecules/100 ev. At the lowest pulse intensity used, G(C6H5OH) = 1.9 molecules/100 ev, which approaches the values found in steady irradiations. Some additional phenol is formed in slow post-irradiation reactions. Diphenyl was identified as a product in the deaerated system by gas chromatographic analysis. Its formation is largely the result of post-irradiation reactions, the initial yield being substantially lower than previously reported. The mechanism of the radiation chemical reaction in both deaerated and oxygenated solutions is discussed on the basis of the conclusion that the hydroxyl radical enters the ring to form the hydroxycyclohexadienyl radical.

The optical absorption spectrum of the solvated electron has been determined by pulse radiolysis in the pure liquid ethers: tetrahydrofuran, methyltetrahydrofuran, diethyl ether, dimethoxyethane, diglyme, triglyme, and tetraglyme. The absorption maxima are at 4720, 4650, 4350, 4880, 5220, 5440, and 5580 cm−1, respectively. The half-widths of the bands have also been measured. The oscillator strength, determined for the first four ethers is approximately unity. The absorption bands have been determined in binary solutions with ethylenediamine and for tetrahydrofuran-water over the entire concentration range. Calculations using a recent form of a cavity-continuum model have been compared with the experimental results. The model shows agreement with the experimental values for the transition energy for an effective cavity radius of about 4 Å and a coordination number of 6 or 8. Kinetics for the attachment of solvated electrons to pyrene and for the reaction of the solvated electron with the solvent counterion have been investigated in several ethers and absolute rate constants determined.

Publication costs assisted by the U. S. Atomic Energy CommissionThe optical absorption band of the sodium cation-electron pair, (Na+ ,es-), in tetrahydrofuran solution has been determined in pulse radiolysis studies. The absorption maximum is at 890 nm at 25", and shows a temperature coefficient of -7 cm-l deg-I. The molar extinction coefficient at the maximum is 2.4 x 1CP M-1 crn-l, and the oscillator strength is f = 1.0. The large shift from the maximum of the solvated electron in THF, which is at 2120 nm, suggests strong coupling with the cation. The absolute rate constant for the reaction of the solvated electron with free sodium cation is 7.9 X 10l1 M-I sec-1, with an activation energy of 1.4 kcal/mol. Rate, constants were also determined for several reactions of esol-with organic molecules. For comparison rate constants for a number of reactions of (Na+,e,-) were also determined. These were found to be roughly an order of magnitude lower than the rate constants for the analogous reactions of esol-. The free-ion yield for esol-, determined using sodium cation as scavenger, was found to be 0.39 molecule/100 eV.

With the recent application of fast infra‐red detection to pulse radiolysis studies of the solvated electron, the optical absorption spectrum has now been observed into the wavelength region beyond 2000 mμ. It has thus been possible to determine the spectrum in such weakly‐polar liquids as tetrahydrofuran, diethylamine and others, and in binary solvent systems of tetrahydrofuran with other liquids. Data now available for a variety of liquids cover an enormous range with the maximum of the absorption band at 580 mμ to 2100 mμ. In the following weakly‐polar liquids the band maxima are: tetrahydrofuran 2100 ± 50, diethylamine 1900 ± 80, dimethoxyethane 1900 ± 150 and diethyl ether 2050 ± 150mμ. It has been shown for such liquids as ammonia and ethylenediamine that results from pulse radiolysis of the pure liquid and from alkalimetal solutions lead to the same absorption band for the solvated electron. In all binary solvent systems studied, only a single absorption band is seen with λmax intermediate to the maxima observed for the pure components. Most of the data suggest that selective solvation in microscopic domains of the individual component does not occur, and the observations do not seem to support those models which propose that the optical properties are determined only by solvation with a small number of molecules. In tetrahydrofuran‐water solutions, however, the water is dominant in determining the optical properties, whereas the tetrahydrofuran is dominant in determining the dielectric properties. There thus appears to be some selective interaction with the water. The data now available for various liquids suggest that the spectral position of λmax is determined by the structural class of the molecule as well as by the dielectric properties of the liquid.

The optical absorption spectra and reaction kinetics of transient species in oxygenated aqueous solutions have been investigated over the pH range 2 to 14 using the pulse radiolysis technique. The HOz radical spectrum has a maximum a t 230 mp with a molar extinction coefficient of e?& = 1150 M-I cm.-' a t 2Fjo. The 02-has a maximum at 240 m p with E%! = 1060 M-I em.-'. The pK of the hydroperoxy radical was found to be 4.5 f 0.2. The absolute rate constants for the bimolecular disappearance of these transients a t 25' were determined to be: kno,+Ho, = 2.7 X lo6 M-' see.-', and k0,-+ 0,-= 1.7 X 107 M -I sec. -l e In alkaline solution above pH 10, two new transient species were observed, one with a maximum at 240 mp, the other with a maximum a t 430 mp. Both species decayed according to a first-order rate law with a pH-dependent half-life, the former in the range of seconds, the latter in the range of milliseconds. The possible identity of these transient species is discussed. IntroductionThe kinetics of the hydroperoxy radical in oxygenated aqueous solutions have recently been studied by several fast reaction techniques.2-6 In these studies the radical has been generated by radiolysis,2j6 by flash phot~lysis,~ and by cheniical means3-4 from the reaction of ceric ion and hydrogen peroxide.In the radiolysis of oxygenated aqueous solutions, the hydroperoxy radical is formed from the reducing species in two different ways