The Spectrum and Other Physical Properties

The intensity of absorption gives the product G , where G is the observed yield and is the molar extinction coefficient. The absolute value of was determined by Fielden and Hart (1967) using an H2-saturated alkaline solution and an alkaline permanganate-formate solution, where all radicals are converted into Mn042. They thus obtained = 1.09 x 104 M- cm1 at 578 nm, which is almost identical with that obtained by Rabani et al. (1965), who converted the hydrated electron into the nitroform anion in a neutral solution of tetrani-tromethane. From the shape of the absorption spectrum and the absolute value of at 578 nm, one can then find the absolute extinction coefficient at all wavelengths. In particular, at the peak of absorption, (720)/ (578) = 1.7 gives at 720 nm as 1.85 X 104 M 1cm 1. 

The oscillator strength for absorption is a very important quantity signifying the nature of the transition. If the absorption spectrum is known, the oscillator strength can be calculated using Eq. (4.20). Instead of numerical integration, one often assumes that the spectrum is approximately gaussian with the same half-width Av (cm-1) as experimentally observed. One then obtains/, the oscillator strength, as 

For the hydrated electron, = 1.85 x 104 M cmr1. Taking the half-width as 

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