The 13C2 and 12C13C Ballik-Ramsay system

The infrared spectrum of the b³Σ⁻ → a³Π Ballik-Ramsay system has been observed for both ¹³C₂ and ¹²C¹³C isotopic species using high-resolution Fourier transform spectroscopy. Twelve bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2, 4 → 2, 4 → 3, 5 → 2, 5 → 3, 6 → 3 of ¹³C₂ and seven bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2 of ¹²C¹³C were identified in the spectral range 3500–12 000 cm⁻¹. Perturbations in the b³Σ⁻ (v = 0, 1, 2, 3) levels were reduced and accurate perturbation parameters derived from the analysis. A comparison with ab initio calculated spin-orbit coupling constants is presented.