Pulse radiolysis of aqueous thiocyanate solutions. Nature of the intermediate transient species

D. Behar, P. L.T. Bevan, G. Scholes

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Abstract

The pulse radiolysis of N2O-saturated aqueous solutions of KCNS has been studied under both neutral and alkaline conditions, and the optical absorption spectra of the precursors of the (CNS)2- radical anion have been obtained. In neutral solution the precursor has λmax 330 nm with ε330 900 M-1 cm-1, while in alkali it has a λmax 390 nm and ε390 4600 M-1 cm-1. Kinetic considerations lead to their assignment as CNS and CNSOH-, respectively. The oxidation of CNS- ions by OH radicals in these solutions is interpreted in terms of the reactions: OH + CNS- → CNSOH-; CNSOH- ⇌ + CNS + OH-, K = 3.2 × 10-2 M; and CNS + CNS- ⇌ (CNS)2-, K = 2 × 105 M-1. The rate constant for the dissociation of CNSOH- has been found to be >5 × 107 sec-1. In alkaline solutions, oxidation of CNS- by O- also takes place, viz., O- + CNS- → CNSO2-, k = 3.7 × 109 M-1 sec-1; CNSO2- + H2O ⇌ CNSOH- + OH-. Under the conditions used (up to 0.8 M NaOH) the doubly charged adduct is converted completely to CNSOH-.

Original languageEnglish
Pages (from-to)1537-1542
Number of pages6
JournalJournal of Physical Chemistry
Volume76
Issue number11
DOIs
StatePublished - 1972
Externally publishedYes

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