The ion species ratios as well as the angular divergences are measured by using a Doppler shift spectroscopy of Hα spectral lines, which originate from several different ions, such as H2+ and H3+ as well as H+, and are spectrally well resolvable from each other on the measured spectral window of detection system. The angular divergences of the ion beam components are determined from the linewidths of the measured emission lines, and the ratio of mixed species is deduced from the intensity ratio of each peak. The ion species ratios measured by the Doppler shift spectroscopy are cross checked by a mass analyzing magnet. The measurements are performed varying the input rf power and the operating source pressure. © 2000 American Institute of Physics.