The addition of H2 to an Ar plasma studied by fast flow glow discharge mass spectrometry (FFGD-MS): mechanism and relative sensitivities

Abstract

Changes in steel and copper cathode ion intensities from the afterglow of a fast flow dc glow discharge (FFGD) have been studied as a function of the amount of H₂ added downstream from the active discharge region. The signals from the majority of different elements increased, although some analytes were actually quenched. In general, the data were qualitatively similar to previous ‘hydrogen effect’ studies using conventional ‘static gas’ GD source designs. Here variations in the size of the effect are reported as hydrogen concentration, plasma density, interaction time and ion extraction voltage were changed independently. It was not possible to rationalise the data obtained using a mechanism based on ion–molecule reactions. The results also indicated that Penning ionisation involving the Ar ³P_2,0 states is probably not the primary mechanism for the ions detected in this kind of flowing plasma. On the other hand, a mechanism based on the Rydberg gas model of the flowing plasma [R. S. Mason, P. D. Miller, I. P. Mortimer, D. J. Mitchell and N. A. Dash, Phys. Rev. E, 2003, 68, 016408] fits well with all the changes observed.