Asymmetric charge transfer with hydrogen ions — An important factor in the “hydrogen effect” in glow discharge optical emission spectroscopy

The effects of traces of molecular gases (H2, N2& O2) in glow discharges in noble gases

“…This effect also occurs for Fe II lines [23], as shown in figure 9, where lines in the Fe II spectrum with a total excitation energy (TEE) (ionisation energy + excitation energy of the ion)~15.8 eV (Group A) are suppressed. Charge transfer (CT) is a resonant process and only small amounts of energy can be converted to or from kinetic energy so the TEE needs to close to the ionisation energy of argon (15.76 eV) or the nearby metastable 2 P 1/2 state (15.94 eV).…”

“…The intensity of bands in the 2 nd positive system of nitrogen also showed marked nonlinearity with increasing hydrogen concentration. Hodoroaba [12] and Steers [23] both reported very non-linear behaviour for the intensity of the Hαand Hβlines (656.2nm and 486.1 nm, respectively); these lines should not be subject to self absorption. It is clear that for both hydrogen and nitrogen, the degree of dissociation is highly dependent on the discharge conditions.…”

“…However, excitation is also possible from the metastable FeI levels close to the ground state, so additional energy levels can be involved. It was observed in 1998 that excitation by hydrogen CT also occurred [23], causing enhanced intensities for FeII states with TEE~13.6 eV. Figure 8(a) shows the ratios of the intensity in an argon/hydrogen mixture to the intensity in pure argon, plotted against the energy of the upper state for a hydrogen concentration of 0.3% v/v, whilst the section of the plot figure 8(b) shows that the marked difference in the relative positions of groups B and C of levels for a hydrogen concentration of 0.08% v/v.…”

“…Hydrogen CT excitation has also been observed in Ti II and Cr II spectra. Reproduced from [23] with acknowledgements to Elsevier…”

Glow discharge excitation and matrix effects in the Zn–Al–Cu system in argon and neon

“…An extensive work about matrix effects related to ACT reactions in an ICP plasma has been recently published by Chan and Hieftje [8,9]. In GD-OES, no literature other than the papers mentioned above exists to my knowledge about excitation-related matrix effects, except of those caused by hydrogen [4,[10][11][12][13][14]16,17], nitrogen [15,16] and oxygen [16,17]. Those studies, however, describe frequently situations in which the light element is introduced into the discharge as an impurity gas, mostly together with argon.…”