An intense slit discharge source of jet-cooled molecular ions and radicals (T-rot<30K)

A novel pulsed, slit supersonic discharge source is described for generating intense jet-cooled densities of radicals (> 10(12)/cm(3)) and molecular ions (> 10(10)/cm(3)) under long absorption path (80 cm), supersonically cooled conditions. The design confines the discharge region upstream of the supersonic expansion orifice to achieve efficient rotational cooling down to 30 K or less. The collisionally collimated velocity distribution in the slit discharge geometry yields sub-Doppler spectral linewidths, which for open-shell radicals reveals spin-rotation splittings and broadening due to nuclear hyperfine structure. Application of the slit source for high-resolution, direct IR laser absorption spectroscopy in discharges is demonstrated on species such as OH, H3O+ and N2H+.