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

Abstract

A sensitive and generally applicable technique for direct absorption spectroscopy on electronic transitions of transient species in the gas phase is presented. The method is based on cavity ring down spectroscopy in a pulsed slit nozzle, incorporating a discharge in a high pressure supersonic expansion. The performance is demonstrated with spectra of the 0 0 0 origin band of the 2 ⌸←X 2 ⌸ electronic transition of the isoelectronic linear carbon chain radicals C 6 H and C 6 H 2 ϩ. Rotationally resolved and rotationally cold spectra (T rot Ͻ15 K͒ have been obtained. The sensitivity of the technique is demonstrated for anions with a detection limit as low as 10 7 C 2 Ϫ molecules cm Ϫ3 for rovibrational transitions of the B 2 ⌺ u ϩ ←X 2 ⌺ g ϩ system.

High-resolution electronic spectroscopy of a nonlinear carbon chain radical C6H4+

“…14 The plasma is generated by a discharge through a gas pulse ͑Ϫ300 V, 30 Hz repetition rate͒ of a 0.5% C 2 H 2 ͑and/or C 2 D 2 ) in He mixture with a backing pressure of 10 bars in the throat of a 3 cmϫ100 m multilayer slit nozzle geometry. Rotational temperatures of the order of 20-40 K are routinely achieved.…”

Mass spectrometric and laser spectroscopic characterization of a supersonic planar plasma expansion

“…The plasma source has been described in detail before [7]. A three-dimensional picture is shown in Fig.…”

“…Such an expansion provides a Doppler free environment and combines high molecular densities and relatively long absorption path lengths with effective adiabatic cooling. During the last decade a number of planar plasma sources has been designed, using discharge [6,7], ablation [8], photolysis [9] and electron ionization [10] tech-niques, with spectroscopic applications ranging from cluster ions [11] to long and highly unsaturated carbon chain radicals [12]. The major disadvantage of such a plasma for spectroscopic use is that a large variety of species is formed simultaneously in the expansion.…”

Broadband Cavity Enhanced Absorption Spectroscopy: A New Approach to Search for DIB Carriers

“…In the present set-up, a pulsed planar discharge expansion of 0.5% C 2 H 2 , diluted in a 1:1 He/Ar precursor gas mixture is employed to form carbon chain transients. The production technique has been described in detail elsewhere (Motylewski & Linnartz 1999) and will only be discussed briefly here, with typical settings for the measurements presented. A supersonically expanding gas pulse of 2 ms is released into a vacuum chamber.…”

“…Molecular beams and jets coupled with discharge (e.g. Motylewski & Linnartz 1999) or laser vaporization/photolysis sources (e.g. Giesen et al 1994) have been used to generate adiabatically cooled transients, as in the diffuse interstellar medium intense radiation fields are expected to favour formation of unstable species.…”