Improved molecular parameters for the Ballik-Ramsay system of diatomic carbon (b^3Σg^− → a^3Πu)

The infrared spectrum of the C2 (b3Σg− → a3Πu) Ballik–Ramsay system was observed in a hollow-cathode discharge source by using a high-resolution Fourier-transform spectrometer. Ten bands with (υ′–υ″) equal to (0–1), (1–2), (2–3), (3–4), (0–0), (1–1), (1–0), (2–1), (3–2), and (4–3) were observed in the spectral region between 3300 and 6500 cm−1. The (3–4) and (4–3) bands were observed for the first reported time. In addition, 360 lines belonging to satellite branches were observed. A global fit of the present data combined with previous high-resolution data in an iterative nonlinear least-square algorithm yields equilibrium molecular parameters with a variance of 0.0051 cm−1. The inclusion of the satellite lines facilitates the direct improvement of the fine-structure parameters. Rotational perturbations were observed in the upper b3Σg− state and were analyzed by using deperturbation methods.