Hydrated Electrons Produced by the Flash Photolysis of Co+, Ni+, Zn+, and Cd+ Ions

Hydrated electrons are produced with a quantum yield of about unity when the low valence state ions Co + , Ni + , Zn + , and Cd + are photolyzed by light within their absorption bands centered at ∼300 nm. The observations seem to offer direct evidence that these absorption bands may be assigned as charge-transfer bands, and specifically as charge-transfer-to-solvent (c.t.t.s.). The ions are probably present as simple aquo complexes, since they were formed initially in very dilute aqueous solution from the divalent sulfate salts; but they may be solvated ion–electron pairs. Cu + ions do not show a similar strong charge-transfer band at any wavelengths >230 nm and the second maximum in the case of Co + at 360 nm is not of the c.t.t.s. type.The experiments used a double flash photolysis method whereby the first flash photolyzed SO 4 2− with light at λ < 220 nm to produce hydrated electrons which then reacted with Co 2+ , Ni 2+ , Zn 2+ , or Cd 2+ ions present at 10 −5 to 10 −6  M. The short-lived monovalent ions so formed were photolyzed 10–300 µs later by the second flash of restricted wavelengths.