The 2Π←X 2Π electronic spectra of C8H and C10H in the gas phase

The (2)Pi<--X (2)Pi electronic transition of linear C8H/C8D and C10H/C10D has been detected in the gas phase. The carbon radical chains were produced at low temperatures in a pulsed slit nozzle, incorporating a discharge in a high pressure expansion. Cavity ring down spectroscopy is used as a sensitive technique to observe the band systems in absorption. The 0(0)(0) band of the (2)Pi(3/2)<--X (2)Pi(3/2) electronic transition of C8H in the gas phase has its origin near 15 973.5 cm(-1) whereas that of C10H is around 14 000 cm(-1). Some transitions involving vibrational excitation in the upper (2)Pi electronic stare have been also detected. These measurements were undertaken because carbon chains are among the appealing candidates as carriers of diffuse interstellar bands; the observed origin bands do not show matches with the hitherto reported wavelengths. However, these gas phase data now provide a firm basis for a specific astronomical search. (C) 1998 American Institute of Physics. [S0021-9606(98)00934-9].