Extreme ultraviolet spectroscopy of helium–hydrogen plasma

Extreme ultraviolet spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q . 13.6 eV, q = 1, 2, 3, 7, 9, 11, or q . 13.6 eV, q = 4, 6, 8 less 21.2 eV corresponding to inelastic scattering of these photons by helium atoms due to excitation of He (1s 2 ) to He (1s 1 2p 1 ). The average hydrogen atom temperature was measured to be 180–210 eV versus ≈3 eV for pure hydrogen. The electron temperature T e for helium–hydrogen was 30 500 ± 5% K compared to 7400±5% K for pure helium. Known explanations for the novel series of spectral lines and extraordinary broadening were ruled out.