Infrared absorption spectroscopy of molecular ions in a corona-discharge slit expansion

A new corona slit nozzle has been constructed to study, by means of direct infrared absorption, molecular ions generated in a continuous supersonic expansion. Spectra of the ions H3+, D2H+, D3+, HN2+, H3O+ and ArH+, were detected in the 1900–3600 cm−1 region using difference frequency and diode laser sources. The new jet source gives a significant improvement in signal-to-noise ratio and a reduction in rotational temperature compared to our previously reported hollow-cathode jet discharge source. The effective rotational and translational temperatures were in the ranges 33–93 and 50–100 K, respectively. The experimental factors influencing the performance of the source are discussed.