A study of the UV—visible absorption spectra of Br2 and BrCl

Abstract

Abstract A mathematical representation of the UV—visible absorption spectrum of Br2 vapour, which is based on a four-band semi-logarithmic gaussian distribution function, was derived in an assessment of the literature spectra where tanhtanh(hc×325.3213 cm−1/2kT and λ is the wavelength in vacuum (200⩽λ⩽650 nm). The UV—visible absorption spectrum of BrCl (200⩽λ⩽600 nm) and the equilibrium coefficient for the reaction (Br2)g + (Cl2)g ← KBrCl → 2(BrCl)g were obtained by analysis of the absorption spectra of gaseous mixtures of Cl2 and Br2, which were investigated at 298 K with a spectral resolution of 0.2 nm. The absorption cross-sections of BrCl are in good agreement with those reported by other workers and can be adequately described by a three-band semi-logarithmic gaussian distribution function where tanhtanh(hc×443.1 cm−1/2kT) and λ is the wavelength in vaccum (200⩽λ⩽600 nm). In contrast with the spectrum of Br2 vapour, no evidence was found for a fourth band in the spectrum of BrCl in the wavelength range studied. The value obtained for the equilibrium coefficient KBrCl(298 K)[BrCl]2/([Br2][Cl2]) = 10.1±1.1 is the largest reported so far. This yields a standard enthalpy for the formation of BrCl of ΔHBrCl°(298 K) = 14 307 J mol−1.