Cavity ring down spectroscopy on radicals in a supersonic slit nozzle discharge

A sensitive and generally applicable technique for direct absorption spectr oscopy on electronic transitions of transient species in the gas phase is p resented. The method is based on cavity ring down spectroscopy in a pulsed slit nozzle, incorporating a discharge in a high pressure supersonic expans ion. The performance is demonstrated with spectra of the 0(0)(0) origin ban d of the (2)Pi <-- X(2)Pi electronic transition of the isoelectronic linear carbon chain radicals C6H and C6H2+. Rotationally resolved and rotationall y cold spectra (T-rot<15 K) have been obtained. The sensitivity of the tech nique is demonstrated for anions with a detection limit as low as 10(7) C-2 (-) molecules cm(-3) for rovibrational transitions of the B(2)Sigma(u)(+) < -- X(2)Sigma(g)(+) system. (C) 1999 American Institute of Physics. [S0034-6 748(99)01002-3].