Re-evaluation of the thiocyanate dosimeter for pulse radiolysis

Abstract

The thiocyanate dosimeter (10^–2 mol dm^–3 SCN^– in O₂-saturated water) has been standardised against the super-Fricke dosimeter (10^–2 mol dm^–3 Fe^II in O₂-saturated 0.4 mol dm^–3 H₂SO₄) using the hexacyanoferrate(II) dosimeter [5 × 10^–3 mol dm^–3 Fe(CN)₆^4– in O₂-saturated water] as a secondary standard. On the basis that G(Fe^III)= 1.67 × 10^–6 mol J^–1 and ε_Fe^III= 220.4 m² mol^–1 at 304 nm and 25 °C in the super-Fricke dosimeter, we obtain Gε[Fe(CN)₆^3–]=(3.47 ± 0.06)× 10^–5 m² J^–1 at 420 nm and Gε(SCN)₂˙^–=(2.59 ± 0.05)× 10^–4 m² J^–1 at 475 nm. These values remain unchanged when the solutions are saturated with air instead of O₂ and are doubled in N₂O-saturated solution.