Far-ultraviolet solution spectroscopy of thiocyanate

Abstract

The far-ultraviolet solution of very dilute thiocyanate ion in a range of solvents shows that there are at least three absorption bands labelled A, D and E. All three bands are shown to have charge-transfer-to-solvent characteristics, in contrast to some previous reports. The conflicting previous reports of the spectroscopy and photochemistry of thiocyanate ions, together with the current work, are resolved in terms of a spectroscopic transition scheme involving a forbidden transition at ca. 36 000 cm^–1, which is normally extremely weak or not detectable. This transition is only detected at high concentrations of salt. The first allowed transition is expected to occur at ca. 62 000 cm^–1. Within this scheme the c.t.t.s. bands occur (in aqueous solution) at 46 000 and 53 500 cm^–1. A further band is observed in red-shifting solvents at ca. 57 000 cm^–1. The temperature sensitivities of the three c.t.t.s. bands, relative to the solvated electron, are 0.58, 0.47 and 0.30.