Transient Raman observation and bond properties of a mixed dihalide radical anion in water.

This article focuses on the identification and characterization of the mixed dihalide radical anion BrCl·− (bromine chloride radical anion) produced in aqueous solutions by radiation-induced reactions. Using time-resolved resonance Raman spectroscopy combined with density functional theory calculations, the study confirms the presence of BrCl·− through its distinct vibrational signature at 212 cm⁻¹, differentiating it from homonuclear dihalide radicals Cl₂·− and Br₂·−. The research further analyzes the reaction pathways and equilibria governing the formation and decay of BrCl·−, explaining its elusive nature and contrasting it with the non-observability of the analogous ICl·− radical due to differing thermochemical equilibria. Structural parameters such as bond lengths, force constants, and dissociation energies of these radicals are reported, providing insight into their ground-state bonding and stability in aqueous environments.