Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

Satoh, K.; Wagatsuma, Kazuaki

doi:10.1016/j.sab.2015.03.015

Cited by 6 publications

(1 citation statement)

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Wagatsuma

Satoh

2016

ANAL. SCI.

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This paper describes a plasma-diagnostic method using an enhancement factor on the Boltzmann distribution among emission lines of iron atom in an argon radio-frequency inductively-coupled plasma (ICP). It indicated that Boltzmann plots of the atomic lines having lower excitation energies (3.4 to 4.8 eV) were well fitted on a straight line while those having more than 5.5 eV deviated upwards from a linear relationship. This observation could be explained by the fact that ICP is not in a complete thermodynamic equilibrium between direct excitation to energy levels of iron atom, ionization of iron atom, and radiative decay processes to the ground state. Especially, the recombination of iron ion with captured electron should accompany cascade de-excitations between closely-spaced excited levels just below the ionization limit, the rates of which become slower as a whole; as a result, these high-lying levels might be more populated than the low-lying levels as if a different LTE condition coexists on the high energy side. This overpopulation could be quantitatively estimated using an enhancement factor (EF), which was a ratio of the observed intensity to the expected value extrapolated from the normal distribution on the low energy side. The EFs were generally small (less than 3); therefore, the cascade de-excitation process would slightly contribute to the population of these excited levels. It could be considered from variations of the EF that the overpopulation proceeded to a larger extent at lower radio-frequency forward powers, at higher flow rates of the carrier gas, or at higher observation heights. The reason for this is that the kinetic energy of energetic particles, such as electrons, becomes reduced under all of these plasma conditions, thus enabling the high-lying levels to be more populated by cascade de-excitation processes from iron ion rather than by collisional excitation processes with the energetic particles. A similar Boltzmann analysis using the EF was also carried out in emission lines of nickel atom, which confirmed the conclusion concerning the atomic lines of iron.

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Section: Introductionmentioning

confidence: 99%