The wavelength dependence of the photodetachment cross section of electrons from O2minus;in liquid tetramethylsilane, 2,2hyphen;dimethlypropane, 2,2,4hyphen;trimethylpentane and argon was measured from the conductivity change induced by a short laser pulse. The O2minus;was generated by exposing a solution of O2to a pulse of 2 MeV x rays just prior to the laser pulse. Comparison with gas phase results from the literature shows that the threshold law is the same in the two phases, and that the size of the cross section is similar at comparable excess energies. However, the thresholds are shifted from the infrared in the gas phase to the visible region in solution. The observed values are:Eth=2.08, 2.02, 2.55 eV in tetramethylsilane, 2,2hyphen;dimethylpropane, and 2,2,4hyphen;trimethylpentane at 296 K, respectively, and 2.32 eV in tetramethylsilane at 200 K. The major energy term causing this shift is the solvation energy of O2minus;. If this is described by Bornrsquo;s equation the effective radius of O2minus;is 1.54plusmn;0.02 Aring; in the hydrocarbons and tetramethylsilane. The threshold observed in argon is 2.43 eV which is attributed to photodetachment from O4minus;. From the observed threshold law it is concluded that the density of states of the conduction band in these liquids has the same (parabolic) shape as in the gas phase. This technique is shown to be useful to measure rate constants for electron transfer in solution.
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