High-resolution laser spectroscopy of the transition of MgC4H

The 0 0 0 band of the A ˜ 2 Π - X ˜ 2 Σ + transition of MgC4H has been recorded at high resolution using laser-induced fluorescence. The molecules were produced using an ablation source by the reaction of magnesium and ∼10% acetylene seeded in helium. The rotationally-resolved high-resolution data were fitted to obtain rotational and fine structure parameters for both states. The centrifugal distortion, upper state Λ-doubling and ground state spin-rotation splitting parameters were all found to be negligible and the reasons for this are investigated and discussed. The 3 0 1 band heads of the A ˜ 2 Π - X ˜ 2 Σ + transition of MgC6H were obtained but the rotational structure was not resolved.