Pulse Radiolysis of Liquids at High Pressures. I. Absorption Spectrum of the Hydrated Electron at Pressures up to 6.3 kbar

A system for study of the pulse radiolysis of liquids at pressures up to 6.9 kbar is described. With this system the optical absorption spectrum of the hydrated electron has been measured at $\text{29 ± 3°}\mathrm{C}$ and applied pressures in the range 0–6.3 kbar. The spectrum shifts monotonically to shorter wavelengths with increase in applied pressure from 0 to 6.3 kbar. The transition energy at the absorption maximum, E_max, increases from 1.71 to 2.00 eV, and the bandwidth at half‐maximum increases by $\text{∼ 28 \%}$ . It is concluded that the extinction coefficient at the absorption maximum decreases by $\text{∼ 18 \%}$ and, therefore, that the oscillator strength shows little or no pressure dependence. Values of E_max obtained in the present work and from a published study of the temperature dependence show a monotonic increase with increase in the static dielectric constant, D_s. It is suggested that the correlation between E_max and D_s is a consequence of a predominant influence on the structure of $e_{\mathrm{aq}}^{-}$ of an attractive force determined by the local dielectric constant of the first solvation shell. Being determined in a similar manner by the same physical factors, D_s and the local dielectric constant change in the same direction.