A kinetic study of the dehydrations of the alums KCr(SO₄)₂. 12H₂O and KAl(SO₄)₂. 12H₂O

By product identification and competition studies with selected solutes it has been shown that the reducing species generated m the ultraviolet photolysis of aqueous iodide ion is the solvated electron. Thus it does not react much more rapidly with O$_2$ than with N$_2$O, it reacts with 1:2-dichloroethane to form chloride (Cl$^-$) and not H$_2$ and reacts readily with I$^-^3$ ion at a rate which increases with ionic strength so that the slope of the Bronsted plot is approximately unity. In solutions with $\mu$ = 0.23 at solute concentrations where e$^-_{aq\ldot}$ reacts in less than 3 x 10$^{-10}$ s there is insufficient time for the ion atmosphere to form and the rate constant diminishes accordingly. The primary quantum yield is greater at 2288 $^\overset{\circ}{\mathrm A}$ than at 2537 $^\overset{\circ}{\mathrm A}$ and at each wavelength it increases markedly with temperature. Evidence is presented that the electron moves rapidly to a distance (of at least 10 $^\overset{\circ}{\mathrm A}$) from the site of its formation and that this process, which occurs when the excited iodide ion dissociates and is not deactivated, involves the rotation of water molecules.