Stimulated-emission pumping spectroscopy study of jet-cooled C₃: Pure bending levels and bend-symmetric-stretch combination levels of X¹Σ^± _g

Stimulated-emission pumping spectra were recorded for many pure bending levels [(0, 2, 0)-(0, 34, 0)] and bendsymmetric-stretch combination levels [(1, 0, 0)-(1, 8, 0) and (3, 4, 0)-(3, 8, 0)] in the state of C3 following excitation of transitions in the A band system. Rotational levels to J = 16 were probed and, because of strong mixing of vibrational angular momentum components, levels with I up to 8 were observed. A rotational analysis was carried out by means of a simple rigid-rotor harmonic-oscillator model for a linear molecule. An adequate fit was obtained, showing that all these vibrational levels could be described by a linear average geometry even though the bending vibration isknown to be of extremely large amplitude. B was found to increase strongly with V2 and todecrease with excitation in vi. Interpretation of the physical meaning of the resulting parameters is difficult, however, since the vibrational potential is not well described bya harmonic oscillator.