Abstract

Ne ii and Ar ii spectral lines from a low-current Au hollow-cathode (HG) discharge are analyzed by a pressure-scanned, Fabry–Perot interferometer that views the HC end-on. A sum of two Voigt functions is used to analyze the experimental interferogram. These functions correspond to a slow-ion group in equilibrium with the neutrals and a fast group that is shifted relative to the slow group. The slow-group temperature Ts is found by analyzing Ne i lines, and the fast-group temperature Tf is found by graphically fitting the weighted sum of two Voigt functions to the Ne ii interferogram. The shift is related to Tf through a relation derived elsewhere, involving an electric field; this field is assumed to be formed in an electric double layer. Tf is approximately constant (2750 K) over a series of Ne ii lines, whereas °NfNs, the ratio of the total number of fast-group ions to the total number of slow-group ions, varies from ≈ 0.20 to 0.78, depending upon the quantum numbers S, L, and J of the upper state. Tf and °NfNs increase with current; Tf remains virtually constant with pressure, whereas °NfNs increases; and at higher pressures Tf remains constant as °NfNs decreases with increasing distance of the emitting region from the center of the HC. The postulated mechanism is that the slow group is formed in a one-step, simultaneous ionization-excitation process from the ground neutral to the upper ionic state, whereas the fast-group ions are formed in a two-step process involving a long-lived ground-state ion accelerated by the field. The observed approximate symmetry of the Ne ii quartet interferograms is attributed to the presence of the 22Ne ions whose isotope shift opposes that of the 20Ne fast-group ions.

© 1974 Optical Society of America

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