DEPARTURES FROM THERMODYNAMIC EQUILIBRIUM IN A HELIUM R.F. DISCHARGE.
YALE UNIV NEW HAVEN CONN OBSERVATORY
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Measurements by Crosswhite and Dieke Am. Inst. Physics Handbook, 1957 of the visible lines of neutral helium emitted in a discharge that was excited by r.f. fields of 15 Mc frequency were used to deduce the population ratios of the various excited states. It is found that the highest states are strongly underpopulated with respect to lower excited states, that there is no significant difference between triplet and singlet populations, and that for any given principal quantum number the S state is highly overpopulated with respect to P and D states. It is concluded that the excitation takes place from the ground state, and that observed population ratios may possibly be used to predict the electron distribution function andor the existence and amplitude of threshold resonances in the excitation cross-sections. Finally, it is pointed out that a discharge of the type discussed may act as a laser in a variety of spectral lines. Author