Preferential excitation of positive molecular ions in a hollow-cathode discharge tube

Abstract

A method of preferential excitation of positive molecular ions in a hollow-cathode DC discharge tube of a special design is described. The anode and cathode columns of this discharge tube are physically separated so that the characteristic emissions from the anode and cathode can be photographed independently. From the examples of the emission spectra of CO, CO+ and CO2+ occurring in the spectral region 210-300 nm and those of N2 and N2+ in the region 334-523 nm, obtained with this tube, it is demonstrated that the cathode emission is a rich source of positive molecular ions and that the anode emission contains almost exclusively neural molecules. Another possible excitation mechanisms for the highly excited states of neutral molecules in the cathode glow is also suggested.