open access

https://hdl.handle.net/2115/97581

Populations of n=2 states of atomic hydrogen in low-density hydrogen plasma : temperature and metastability of 2s 2S1/2

英語

metastability

2025-04-09

IOP Publishing

Plasma Sources Science and Technology

34(4)

045006

The populations of the 2s(2)S(1/2) , 2p(2)P(1/2), and 2p(2)P(3/2) states of atomic hydrogen were examined in a low-density inductively coupled hydrogen plasma using diode laser absorption spectroscopy at the Balmer-alpha line. The Doppler broadened absorption spectra were not fitted with the theoretical spectra under the assumption that the population distribution of the three states followed the statistical weights. The fitting accuracy improved when the population ratio was allowed to deviate from the statistical weights; however, the improvement remained insufficient, especially for spectra observed at low electron densities and low hydrogen pressures. A reasonable fit was achieved only when a high-temperature component was introduced into the velocity distribution function of the 2s(2)S(1/2) state. It was considered that the high-temperature component was produced via the electron-impact dissociative excitation of molecular hydrogen, because the population of the high-temperature component was proportional to the electron density. The experimental results clearly indicated a decrease in the population of high-temperature 2s(2)S(1/2) with increasing electron density and hydrogen pressure. This trend is qualitatively reasonable considering the collisional transfer from the 2s(2)S(1/2) to the 2p(2)P(1/2) and 2p(2)P(3/2) states. However, the cross-sections of the collisional transfer were insufficiently small to explain the experimental observations quantitatively. In addition, the experimental results suggest lower metastability of low-temperature 2s(2)S(1/2) than that of the high-temperature component, which cannot be explained by collision cross-sections. Thus, a more sophisticated model should be investigated in future studies to obtain a deeper understanding of the kinetics governing the 2s(2)S(1/2), 2p(2)P(1/2), and 2p(2)P(3/2) states.

学術雑誌論文

Accepted Manuscript

This is the Accepted Manuscript version of an article accepted for publication in Plasma Sources Science and Technology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6595/adc483.

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