High-resolution Raman spectroscopy in the red and near infrared—II: Vibrational frequencies and molecular interactions of halogens and diatomic interhalogens

Abstract

The Raman frequencies of a series of diatomic halogen and interhalogen molecules in the liquid state and in different solvents are reported. The measurements were carried out on spectra excited in the red and near-infrared spectral range by helium or rubidium radiations, and photographed under high or medium dispersion. The results are tabulated together with the values Δ G 1 2 as obtained from band spectra for the isolated molecules and with available data from infrared absorption measurements and from simultaneous transitions. In comparison to the frequencies to be expected for the non-associated molecules, the observed values show a marked decrease, due to interactions between identical molecular species, or to solute-solvent interactions. Interactions of the latter kind lead, in some cases, to the formation of loose charge-transfer complexes with the solvent acting as donor, and, consequently, to a more pronounced change of frequency of the accepting halogen. The origin of still larger effects, observed on solutions in pyridine, is discussed.