The 1.66 μm Spectrum of the Ethynyl Radical, CCH

Microwave astronomy has identified the Ethynyl radical, CCH, as an important precursor to the creation of polyaromatic hydrocarbons particularly in star-formation regions in space. We report high resolution measurements in the near-IR, close to 1.66 μm by frequency-modulated diode laser transient absorption spectroscopy. Two parallel bands were observed in the recorded spectra. The first originating from the ground X ²Σ⁺ state to a ²Σ⁺ level at 6055.6 cm^-1. The second originates from the first excited bending vibrational level of ²Π symmetry to a ²Π level at 6413.5 cm^-1. Neither of these bands have been previously observed. Parameters from an effective Hamiltonian representing rotational and fine structure levels, useful to up to J = 37/2 and J 29/2 for each band respectively have been obtained. The bands may well be useful for future near-IR astonomy.