Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the Fricke dosimeter

Abstract

In aqueous solution OH radicals react with chloride ions to form initially ClOH^–, the rate constant being 4.3 ± 0.4 × 10⁹ l. mol^–1 s^–1. The rate constant for the dissociation of ClOH^– back to OH radicals and chloride ions is 6.1 ± 0.8 × 10⁹ s^–1. ClOH^– is converted to chlorine atoms via the reaction, ClOH^–+ H⁺→ Cl + H₂O (k= 2.1 ± 0.7 × 10¹⁰ l. mol^–1 s^–1 at an ionic strength of unity), the rate constant for the reverse reaction being 1.3 × 10³ l. mol^–1 s^–1(0.3–3.0 × 10³ l. mol^–1 s^–1). Chlorine atoms combine with chloride ions to form Cl^–₂(k= 2.1 × 10¹⁰ l. mol^–1 s^–1), the rate constant for the dissociation of Cl^–₂ back to chlorine atoms and chloride ions being 1.1 ± 0.4 × 10⁵ s^–1.

The absorption spectra of ClOH^– and Cl^–₂ have been measured in the range 230–450 nm. Cl^–₂ absorption has a maximum at 340 nm where the extinction coefficient is 8.8 ± 0.5 × 10³ l. mol^–1 cm^–1, whereas ClOH^– has a maximum at 350 nm with an extinction coefficient of 3.7 ± 0.4 × 10³ l. mol^–1 cm^–1.

The reactions of chlorine atoms and Cl^–₂ with ferrous ions have also been investigated and the constants are 5.9 ± 0.6 × 10⁹ and 1.4 ± 0.2 × 10⁷ l. mol^–1 s^–1(ionic strength = 0.1 mol l.^–1) respectively. The effect of chloride ions on the mechanism of the Fricke dosimeter is discussed.