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 T_{s} is found by analyzing Ne i lines, and the fast-group temperature T′_{f} is found by graphically fitting the weighted sum of two Voigt functions to the Ne ii interferogram. The shift is related to T′_{f} through a relation derived elsewhere, involving an electric field; this field is assumed to be formed in an electric double layer. T′_{f} is approximately constant (2750 K) over a series of Ne ii lines, whereas °N′_{f}/°N_{s}, 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. T′f and °N′_{f}/°N_{s} increase with current; T′_{f} remains virtually constant with pressure, whereas °N′_{f}/°N_{s} increases; and at higher pressures T′_{f} remains constant as °N′_{f}/°N_{s} 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 ^{22}Ne ions whose isotope shift opposes that of the ^{20}Ne fast-group ions.

V. K. Saini, P. Kumar, S. K. Dixit, and S. V. Nakhe Appl. Opt. 53(19) 4320-4326 (2014)

References

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Variations of a′, T_{f}′, X, and °N_{f}′/°N_{s} with Ne ii transitions. HC = Au- 13/64, I =24 mA, P_{f} = 5.7 torr, and the measured T of Ne i 3520 Å = 990 K.

The T_{s} values differ slightly from the 990 K of Ne i 3520 Å because of the limitations of the graphical method.
The indicated uncertainty for each datum is the average deviation from two pairs of interferograms, each pair of two orders being run on a different day. This random error does not include the effect of the uncertainty in l_{0}, k^{+}, or T_{s}. whose average deviation is ≈±50 K. Typically, for T_{f}′ = 2900 K and a′ = 0.62, a variation in T_{s} of −50 K produces a ΔT_{f}′ = −100 K and a Δa′ = +0.04.

Table II

Variations of a′, T_{f}′, T_{s}, V_{c−a}, X, °N_{f}′/°N_{s} with I. HC = Au-13/64, P_{f} = 3.3 torr, λ = Ne ii 3694 Å, r = 0.

Note that most of the contribution to the V_{c−a} is due to the radial dark-space field, which may explain the inverse variation of X_{calc} with V_{c−a}.

Table IV

Variations of a′, T_{f}′, and °N_{f}′/°N_{s}, with r at low P_{f}. HC = Au-1/2, I = 45 mA, P_{f} = 2.0 torr, λ = Ne ii 3694 Å.

These values correspond to the measured T of Ar i 4511 Å (1370 ± 60 K), and the slight variations therefrom are due to the need to make multiple use of certain basic graphs in the graphical analysis.
Because of the negligible variation of a′ with r near the center of the HC, these values are also representative of the center region.

Table VI

Measured ratios of the peak and of the FWHM and the isotope displacement ID of the decomposed “violet” shoulder of several doublet Ne ii lines.

The ID is to the violet and is relative to the center of the main component (see Fig. 9).

Table VII

Variations of °N_{f}′/°N_{s} with the quantum number J_{upper} of several Ne ii lines, radiating from the Au-1/2 HC at I = 45 mA. The lower and upper terms are of the form ^{4}P–^{4}P°.

Each measurement is an average over two orders.
Since °N_{f}′/°N_{s} varies so slowly with r at the center, its value for this experiment is characteristic of r = 0.

Tables (7)

Table I

Variations of a′, T_{f}′, X, and °N_{f}′/°N_{s} with Ne ii transitions. HC = Au- 13/64, I =24 mA, P_{f} = 5.7 torr, and the measured T of Ne i 3520 Å = 990 K.

The T_{s} values differ slightly from the 990 K of Ne i 3520 Å because of the limitations of the graphical method.
The indicated uncertainty for each datum is the average deviation from two pairs of interferograms, each pair of two orders being run on a different day. This random error does not include the effect of the uncertainty in l_{0}, k^{+}, or T_{s}. whose average deviation is ≈±50 K. Typically, for T_{f}′ = 2900 K and a′ = 0.62, a variation in T_{s} of −50 K produces a ΔT_{f}′ = −100 K and a Δa′ = +0.04.

Table II

Variations of a′, T_{f}′, T_{s}, V_{c−a}, X, °N_{f}′/°N_{s} with I. HC = Au-13/64, P_{f} = 3.3 torr, λ = Ne ii 3694 Å, r = 0.

Note that most of the contribution to the V_{c−a} is due to the radial dark-space field, which may explain the inverse variation of X_{calc} with V_{c−a}.

Table IV

Variations of a′, T_{f}′, and °N_{f}′/°N_{s}, with r at low P_{f}. HC = Au-1/2, I = 45 mA, P_{f} = 2.0 torr, λ = Ne ii 3694 Å.

These values correspond to the measured T of Ar i 4511 Å (1370 ± 60 K), and the slight variations therefrom are due to the need to make multiple use of certain basic graphs in the graphical analysis.
Because of the negligible variation of a′ with r near the center of the HC, these values are also representative of the center region.

Table VI

Measured ratios of the peak and of the FWHM and the isotope displacement ID of the decomposed “violet” shoulder of several doublet Ne ii lines.

The ID is to the violet and is relative to the center of the main component (see Fig. 9).

Table VII

Variations of °N_{f}′/°N_{s} with the quantum number J_{upper} of several Ne ii lines, radiating from the Au-1/2 HC at I = 45 mA. The lower and upper terms are of the form ^{4}P–^{4}P°.

Each measurement is an average over two orders.
Since °N_{f}′/°N_{s} varies so slowly with r at the center, its value for this experiment is characteristic of r = 0.