The A 3Σ−–X 3Σ− electronic transition of HC6N

A combined matrix and gas phase study is presented to identify the A 3Σ−–X 3Σ− electronic transition of the linear triplet isomer of HC6N and isotopic derivative DC6N. Absorption spectra have been observed in a 6 K neon matrix after mass selective deposition and in the gas phase by cavity ring down spectroscopy through a supersonic planar plasma. The band origin of the 000 A 3Σ−–X 3Σ− electronic transition of HC6N is determined to be at 21 208.60(5) cm−1, shifted ∼30 cm−1 to the blue of the neon matrix value. Rotational analysis indicates that the chain is slightly stretched on electronic excitation, yielding B0′=0.027 92(5) cm−1. Transitions to vibrationally excited levels in the upper A 3Σ− state are observed as well. The results are compared with a rotationally resolved spectrum of the 000 A 3Σu−–X 3Σg− electronic transition of the isoelectronic HC7H species.