AbstractThe first observation of inverted population density due to a double electron capture process has been performed for He plasma in contact with H2 molecular gas in the TPD-II device. Recently, the process He2+ + H2 → He∗ (1s3l) + 2H+ has been found to have a very large cross-section (10−15 cm2 or more) in collisions at low energies (below 1 eV) due to an orbiting effect and accidental resonance. To see the population density of He I levels, a 2 m vacuum UV monochromator was used and resonance spectra (np1P → 1s1S, n = 2,3) were measured. In contrast to the quick disappearance of the transition 2p1P → 1s1S of He I, the transition 3p1P → 1s1S has exhibited a noticeable increase of one order of magnitude associated with the injection of H2 gas. As a result, population inversion between 2p1P and 3p1P was concluded to have occurred.
TPD-II装置において、HeプラズマとH₂分子ガスとの接触による二重電子捕獲過程に起因する反転分布の初めての観測が行われた。最近、衝突エネルギーが1 eV以下の低エネルギー領域において、He²⁺ + H₂ → He∗ (1s3l) + 2H⁺という過程が、軌道効果と偶然共鳴により、10⁻¹⁵ cm²以上の非常に大きな断面積を持つことが見出された。He I準位の粒子密度を調べるため、2 m真空紫外分光器を用いて、共鳴スペクトル（np¹P → 1s¹S、n = 2, 3）が測定された。H₂ガス注入に伴い、He Iの2p¹P → 1s¹S遷移が急速に消失するのとは対照的に、3p¹P → 1s¹S遷移は1桁の顕著な増加を示した。この結果から、2p¹Pと3p¹Pの間で反転分布が生じたと結論づけられた。