LIF spectroscopy of the MgCCH free radical

We report first observation of the electronic spectrum of the free radical MgCCH. This molecule was prepared in a supersonic expansion by laser ablation of magnesium in the presence of methane. A strong laser-induced fluorescence excitation spectrum was found in the 415–440 nm region and was assigned to part of the Ã2Π−X̃2Σ+ system. The spectrum is dominated by a single vibrational progression of interval 552 cm−1 which has been assigned to the MgC stretch in the à state. A prelimiry rotational analysis has shown that the rotational constant, BO, in the Ã2Π state is larger than that in the X̃2Σ+ state, indicating a stronger MgC bond in the excited electronic state.