Cavity ring down laser spectroscopy of the transition of CaCCH

While both the A ˜ 2 Π – X ˜ 2 Σ + and C ˜ 2 Δ – X ˜ 2 Σ + transitions of CaCCH have been previously reported in laser-induced fluorescence experiments, the B ˜ 2 Σ + – X ˜ 2 Σ + transition has remained undetected by this technique. We have applied cavity ring down laser spectroscopy to a pulsed molecular jet containing CaCCH, and have observed an absorption feature that does not fluoresce upon excitation, consistent with the B ˜ 2 Σ + – X ˜ 2 Σ + transition.