The photochemistry of aqueous solutions of Fe (II) - I. Photoelectron detachment from ferrous and ferrocyanide ions

Nitrous oxide has been used as a specific scavenger of aquated electrons produced by photo-detachment from Fe2+aq. (hv→Fe3+aq. + e¯aq.) and Fe(CN)4–6 (hv→ Fe(CN)3–6 + e¯aq.) by light of wavelength 2537 Å. In each case Ф(N2) increases to a limiting value as [N2O] is increased; it is 0·07 for the former process and 0·66 for the latter. Use of isopropanol instead of N2O in the latter case indicated that no H atoms are formed in the primary act. Competition experiments indicate that k(e¯aq. + H+) / k(e¯aq. + N2O) =1·86 ± 0·12 when Fe2+aq. is used as the electron source and 1·55 ± 0·1 when lanthanum ferrocyanide is used. For the K4Fe(CN)6 solutions, 2Ф(N2)=Ф(Fe(CN)3–6) unless KCN is present when OH+CN¯→OH¯+CN and Fe(CN)3–6 + CN → C2N2 + Fe(CN)5H2O3¯ (+CN¯→ Fe(CN)4¯6 + H2O) occur. The slopes of the Brønsted-Bjerrum plot for log10k(e¯aq. + NO¯2) is much larger (2 to 2·7) than expected or is obtained from radiation chemical experiments and is explained by a model in which e¯aq. reacts with NO¯2 while still within the relaxed ion atmosphere of the ferrocyanide ion. Other experimental and theoretical evidence is added in support of this hypothesis.