B. Bockrath, J. F. Gavlas, and L. M. Dorfman
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J. V. ACRIVOS.Yes. U. SCHINDEWOLF. The evidence of M- cannot be doubted any more under certain experimental conditions so I raise the question about H-; is it stable in the solutions and does it absorb light as Na-, K-,etc., do? During electrolysis in, e.g., ether between two sodium electrodes, will sodium dissolve at the cathode forming anions or at the anode forming cations or on both sides? Comment: Pulse radiolysis should be done in connection with polarography to get other than optical evidence for M- formation; it also would yield redox potentials.
J. W. FLETCHER. H- is not stable in these solutions. J. L. DYE. The major remaining difference between the results of pulse radiolysis and of metal solution studies is the difference in the ir band of e,- and of metal solutions with crown or cryptand present. This may tell us something about the nature of the species in the latter case. We must remember that the metal solutions are several orders of magnitude more concentrated in the reducing to species M )than in pulse radiolysis so we may have eZ2- or e-.Me- or other spin-paired species.
Spectra of the Solvated Electron Coupled with Metal Cations. Lithium in Tetrahydrofuran Bradley Bockrath, James F. Gavlas, and Leon M. Dorfman' Department of Chemistry, The Ohio State University, Columbus, Ohio 43210 (Received July 23, 1975) Publication costs assisted by the U.S.Energy Research and Development Administration
Our purpose in this paper is to present some recent data on the aggregation of the solvated electron with alkali metal cation for one specific system, namely lithium in tetrahydrofuran. We had reported earlier1 the results of pulse radiolysis investigations of the nature of the aggregation of esol- with sodium in ethylenediamine. More recently, the solvated electron in tetrahydrofuran2 and its ion pair with sodium3 were reported from our laboratory. Coupling of esol- with K+ and with Cs+ has been reported by Salmon et al.4 In their work4 it was concluded that, although the ion pair (Li+,esol-) might be formed, its spectrum in tetrahydrofuran was indistinguishable from that of esol-. We find: to the contrary, that the ion pair (Li+,esol-) formed in tetrahydrofuran exhibits an absorption band with maximum a t 1180 nm. The molar extinction coefficient a t the maximum is 2.3 X lo4 M-' cm-l, which gives an oscillator strength of 0.9 for the band. This absorption band is shown in Figure 1, in which data for three lithium salts, LiC104, LiBr, and LiC1, obtained by two investigators, are seen to clearly define the band. Evidence for the identity of this band has been p r e ~ e n t e d Because .~ of the similarity of this band to that of (K+,esol-),4we have taken the trouble to show, by atomic absorption analyses, that the potassium content of the solutions was below 0.04 ppm and could not possibly have entered into observable reaction on the time scale of our experiments. The absorption maximum of 1180 nm for (Li+,esol-) may be compared with 890 nm for ~ o d i u m1125 , ~ nm for potassiI
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SPECTRUM of
Ll+,e;
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um? 1400 nm for cesium: and 2120 nm for the solvated electron* itself in THF. The smaller shift, from esol-, for Li+ than for Na+ may be the result of a greater degree of solvation of the former cation in T H F than of the latter. Absolute rate constants for the reaction of (Li+,esol-) with anthracene, biphenyl, and dibenzylmercury in THF, at 25OC, were found to be 2.65 X 1O1O, 1.00 X lolo, and 1.8 X 1O1O M-' sec-l, respectively. The latter two values are twofold higher than the corresponding rate constants for (Na+,esol-)3y6 and an order of magnitude lower than the corresponding rate constant^^,^ for esol-.
Acknowledgment. This work was supported by the United States Energy Research and Development Administration. References and Notes (1) J. L. Dye, M. G. DeBacker, J. A. Eyre, and L. M. Dorfman, J. Phys. Chem., 76, 839 (1972). (2) L. M. Dorfman, F. Y. Jou, and R. Wageman, Ber. Bunsenges. Phys. Chem., 75, 681 (1971). (3) B. Bockrath and L. M. Dorfman, J. Phys. Chem., 77, 1002 (1973). (4) G. A. Salmon, W. A. Seddon, and J. W. Fletcher, Can. J. Chem., 52, 3259 (1974). (5) 6.Bockrath and L. M. Dorfman, J. Phys. Chem., 79, 1509 (1975). (6) 6. Bockrath and L. M. Dorfman, J. Am. Chem. SOC.,96, 5708 (1974)
Discussion J. W. FREEMAN. The mobility of electrons in the cyclic polyether p-dioxane is lower than that in n-alkyl ethers. This seemed surprising in view of the relatively low dielectric constant of p-dioxane. The low mobility indicated that the optical absorption spectrum in the latter should lie at a higher energy than those in n-alkyl ethers. F.-Y. Jou recently measured the spectra and verified the prediction. This indicates that there is an unusual interaction between electrons and cyclic polyethers. It might not be necessary to postulate (e-)2,sol to explain the spectrum shift in the presence of crown ethers. A. M. KOULKES-PUJO.Have you tried the pulse radiolysis in presence of a crown compound and is there any shift of the position of ,A, of e,-? L. M. DORFMAN.Yes, no shift.
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15 FREQUENCY ( C M - ' x
Flgure 1.
The Journal of Physical Chemistry, Vo/. 79, No. 26, 1975
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Comment by A. M. K-PUJO. We obtained a similar result for pulse radiolysis of aqueous solutions in the presence of 2,2,2 cryptand. We added it to try to scavenge either HzO+ or H30' formed by ionization process. There is no shift in the position of the maximum of eaq-, but the G value seems to be markedly increased. This work is in progress.
