A Pulsed Hollow Cathode Discharge Operated in an Ar/N₂/O₂ Gas Mixture and the Formation of Nitric Oxide

A hollow cathode discharge with a CuNi (Cu50Ni50) cathode was operated in an Ar/N-2/O-2 gas mixture. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Formation of singly ionised Ar+ and of Cu+ and Ni+ ions is observed in pure argon. With the addition of N-2 or O-2 gas the additional formation of molecular N-2(+) or O-2(+) ions is observed. The intensity of these ions is reduced in the Ar+N-2+O-2 gas mixture and molecular NO+ ions become the most abundant ionic species. The formation of neutral NO molecules is confirmed by optical emission spectroscopy. Gas samples collected at the exhaust of the vacuum chamber confirm the formation of NO and, additionally, of NO2 molecules.