Boltzmann statistical consideration on the excitation mechanism of iron atomic lines emitted from glow discharge plasmas

Estimation Using an Enhancement Factor on Non Local Thermodynamic Equilibrium Behavior of High-lying Energy Levels of Neutral Atom in Argon Radio-Frequency Inductively-Coupled Plasma

“…In this experiment, 45 emission lines of iron atom having excitation energies from 3.37 to 6.87 eV, were chosen in a wavelength range of 368 -384 nm. The details were published in our previous paper, 12 where the transition probability for all of the Fe I lines were included. An energy level table complied by Suger and Corliss 15 was referred to for their assignments, and their transition probabilities were cited from a wavelength table published by Wiese et al 16 These Fe I lines are classified into three groups: 3d 7 4p-3d 7 4s, 3d 6 4s4p-3d 7 4s (3d 6 4s 2 ), and 3d 6 4s4d-3d 6 4s4p optical transitions.…”

“…On the other hand, our previous study on an argon glow discharge plasma (GDP) indicated a large overpopulation of the high-lying excited levels of iron atom, in which several of the EFs exceeded 100. 12 Indeed, the deviation from the LTE condition would be limited to a small extent in the ICP, for which the reason is that the direct excitation by energetic electron, as indicated in Eq. (1), could work as a dominant mechanism in the whole range of the excitation energy, whereas the GDP was in a non-LTE condition, where the high-lying levels of iron atom are less populated through electron collisions due to lower kinetic energy as well as lower number density of electrons in the negative glow region compared to ICP.…”

“…12,13 A large overpopulation was observed in the high-lying excited levels of iron atom in both the argon and neon glow plasmas. It was suggested that this effect would be attributed to recombination/step-wise de-excitations from iron ion that was favorably populated through Penning-type collisions with metastable atoms of argon or neon, rather than collisions with fast electrons.…”

“…It was suggested that this effect would be attributed to recombination/step-wise de-excitations from iron ion that was favorably populated through Penning-type collisions with metastable atoms of argon or neon, rather than collisions with fast electrons. 12 We also investigated Boltzmann plots of iron ionic lines in a nitrogen microwave-induced plasma 14 as well as the glow discharge plasmas, 13 and found abnormal behaviors of these plots that could be explained by charge-transfer collisions with the plasma gas species. In our previous studies, an enhancement factor, which was defined as a ratio of the observed intensity to the expected value extrapolated from a corresponding linear Boltzmann plot, could provide quantitative information on the excitations of the high-lying excited levels.…”

Excitation Processes in Introduction of Bias Current to a Radio-frequency Glow Discharge Plasma Evaluated from Boltzmann Plots of Iron Atomic and Ionic Spectral Lines

“…However, we have reported that the Boltzmann plots can be fitted on linear relationships in the case of both neutral and singly-ionized iron atoms having relatively small excitation energies, implying that their excitations would be controlled principally by energetic particles having Maxwell-like energy distribution, which probably are electrons in the negative glow region. 12,13 In this paper, we investigate Boltzmann plots for emission lines of iron neutral atoms as well as singly-ionized atoms when the bias current is introduced, in order to determine the influence of the bias-current on the electron energy distribution in the plasma. A study on the reason why the bias current enhances the emission intensity of particular emission lines is available.…”