Numerical study of selective double-electron capture by α particles in collisions with hydrogen molecules in a cooled plasma

A numerical study based on a collisional radiative model is performed to understand the enhanced He I (n = 3 → n = 2) line intensities recently observed in an He plasma in contact with hydrogen gas: accidental resonant double-electron capture into the excited states by α particles in the process He2+ + H2 → He∗ (1s3l) + H+ + H+ whose cross-sections are very large at low energies. The calculated results agree fairly well with the observed temporal evolutions of the enhanced He I line intensities.