Resonance Raman and electronic spectra of different salts of the [AuBr4]– ion

Abstract

Three different salts of the [AuBr₄]^– ion display the resonance Raman effect when irradiated in the solid state with any one of several different exciting lines (frequency ν_o). For 457·9 nm excitation, which approximately coincides in frequency with that of an intense electronic band maximum (ν_e) of the anion, the resonance is most effective, with high-intensity overtone progressions in the ν₁(a_1g) fundamental extending as far as the ninth harmonic. For each salt, two other progressions in the ν₁(a_1g) fundamental have also been observed, viz. ν₂+nν₁ and ν₄+nν₁, where ν₂(b_1g) is an AuBr stretching fundamental, and ν₄(b_2g) is a BrAuBr bending fundamental. The members of each overtone progression decrease in intensity and increase in half-bandwidth with increase in the vibrational quantum number. The relationship between the overtone intensities and ν_e–ν_o is detailed. The observation of various overtone progressions has permitted the determination of the spectroscopic constants ω₁ and x₁₁ for the [AuBr₄]^– ion in each crystalline environment.