The 1Πu←X 1Σg+ electronic spectrum of C5 in the gas phase

The origin and three vibronic bands of the (1)Pi(u)<-- X (1)Sigma(g)(+) electronic transition of linear C-5 have been observed in the gas phase. The carbon chain is produced in a slit nozzle employing both discharge and ablation techniques. Cavity ring down spectroscopy is used to measure the electronic transition. The origin band is found at 510.94(1) nm, shifted 29 cm(-1) to the red of the value in a neon matrix. Intramolecular processes lead to broadening and irregularities in the rotational structure. The relation to astronomical observations is discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)03138-4].