High-resolution laser spectroscopy of the (A)over-tilde2Π-(X)over-tilde2Σ+ transition of MgCCH

The 0(0)(0) and 3(0)(1) bands of the (A) over tilde (2)Pi-(X) over tilde (2)Sigma(+) 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 (2)Pi(a)-(2)Sigma(+)(b) Hamiltonian, with standard deviations of 0.0025 cm(-1) (0(0)(0)) and 0.0028 cm(-1) (3(0)(1)).the Lambda-type doubling constants p and q in the (A) over tilde (2)Pi state are unexpectedly positive, indicating that interaction between (A) over tilde (2)Pi and the next highest (2)Sigma(+) 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. (C) 2004 Elsevier Inc. All rights reserved.