High-resolution laser spectroscopy of the A˜2Π-X˜2Σ+ transition of MgCCH

The 000 and 301 bands of the A˜2Π-X˜2Σ+ electronic transition of the MgCCH radical have been recorded at low and high resolution using laser-induced fluorescence. The molecules were created in a laser ablation/molecular beam source through reaction of magnesium atoms ablated from a solid rod with methane gas entrained in helium. The rotationally resolved high-resolution data were fit to a 2Π (a)-2Σ+ (b) Hamiltonian, with standard deviations of 0.0025 cm−1(000) and 0.0028 cm−1(301). The Λ-type doubling constants p and q in the Ã2Π state are unexpectedly positive, indicating that interaction between Ã2Π and the next highest 2Σ+ state is not the dominant cause of the doubling, as was assumed in the structurally similar molecules CaCCH, CaOH, and SrOH in which p and q are larger and negative.