Far-ultraviolet solution spectroscopy of the bromide ion

Abstract

The far ultraviolet absorption spectra of the bromide ion have been studied in a large variety of solvents and over a wide range of temperatures. The solvents used include those which are strongly red-shifting or blue-shifting, relative to water, for charge-transfer-to-solvent (c.t.t.s.) transitions. For some solvents measurements could be made down to ∼165 nm (60 600 cm^–1). A number of new absorption bands have been observed in addition to characterising the previously observed spectra. The experimentally determined spectra are shown to be envelopes composed of overlapping absorption bands which have been deconvoluted using log-normal band shapes, whenever possible. Sets of band pairs have been identified from the spectral resolution and labelled A₁/A₂, B₁/B₂. There is some evidence for further members of the series. The first characteristic doublet, A₁/A₂, has a band separation very close to the doublet splitting of the bromine ²P_½²P atomic states in the gas phase. The B₁/B₂ band pair has a lower doublet separation. These band pairs have strong c.t.t.s. character as shown by their temperature and solvent sensitivities. Further bands are observed at higher energies. These band systems have been correlated on the basis of solvent shifts, doublet band splittings and temperature coefficients. The nature of the bands is discussed and tentative assignments suggested.