Rydberg gas theory of a glow discharge plasma: II. Electrode kinetics (probe theory) and the thermal rate constant for Symmetrical charge transfer involving Rydberg atoms of Ar

Mason, Rod S.

doi:10.1039/b918081h

Cited by 3 publications

(1 citation statement)

References 10 publications

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“…So far, it is still not clear if this improvement by two orders of magnitude might be attributed to a selective loss of Ar ions and/or to a transport improvement of analyte ions by the much higher gas flow rates. [80][81][82] The extremely high ion signal that the detector is able to collect for the matrix elements, which can be as high as 10 12 cps, might restrict its capabilities to determine low signals from trace elements with similar mass to charge ratios. In this case, the abundance sensitivity, which is typically defined as the ratio of a strong signal at a specified m/z, to the contribution that same signal makes one unit above or below the same m/z, is becoming a significant issue.…”

Section: Spectral Interferencesmentioning

confidence: 99%

Glow Discharge Mass Spectrometry

Venzago

Pisonero

2014

Sector Field Mass Spectrometry for Elemental and Isotopic Analysis

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GDMS is based on a glow discharge ion source, which generates ions through sputtering (cathodic sputtering) of a solid surface and ionisation (electron impact or Penning ionisation) by a glow discharge plasma. A glow discharge plasma is formed by the passage of an electric current through a low-pressure gas. The ions are separated in a mass spectrometer and finally recorded at a detector. GDMS is a method for the direct determination of trace elements in solid states providing traceelement information of solid samples. Beside the direct current (DC) mode, analytical glow discharges can also be operated in a radiofrequency (RF) mode, most often applied for analysis of nonconducting samples (Figures 13.1 and 13.2).

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Section: Spectral Interferencesmentioning

confidence: 99%

Glow Discharge Mass Spectrometry

Venzago

Pisonero

2014

Sector Field Mass Spectrometry for Elemental and Isotopic Analysis

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Rydberg gas theory of a glow discharge plasma: I. Application to the electrical behaviour of a fast flowing glow discharge plasma

Mason

Mitchell

Dickinson

2010

Phys. Chem. Chem. Phys.

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Current-voltage (I-V) curves have been measured, independent of the main discharge, for electricity passing through the steady state fast flowing 'afterglow' plasma of a low power dc glow discharge in Ar. Voltage profiles along the axial line of conduction have been mapped using fixed probes and potentiometry, and the mass spectra of cations emerging from the downstream sampling Cone, also acting as a probe anode, were recorded simultaneously. Floating double probe experiments were also carried out. The electrical behavior is consistent with the well established I-V characteristics of such discharges, but does not comply with classical plasma theory predictions. The plasma decays along the line of conduction, with a lifetime of approximately 1 ms, despite carrying a steady state current, and its potential is below that of the large surface area anode voltage; a situation which cannot exist in the presence of a conventional free ion-electron plasma, unless the electron temperature is super cold. Currents, large by comparison with the main discharge current, and independent of it, are induced to flow through the downstream plasma, from the Anode (acting as a cathode) to the anodic ion exit Cone, induced by electron impact ionisation at the anode, but without necessarily increasing the plasma density. It appears to be conducted by direct charge transfer between a part of the anode surface (acting as cathode to the auxiliary circuit) and the plasma, without secondary electron emission or heating, which suggests the direct involvement of Rydberg atom intermediates. The reaction energy defect (= the work function of the electrode surface) fits with the plasma potential threshold observed for the cathodic reaction to occur. A true free ion-electron plasma is readily detected by the observation of cations at the anode surface, when induced at the downstream anode, at high bias voltages, by the electron impact ionisation in the boundary region. In contrast to the classical model, the complex electrical (and mass spectrometric) behaviour fits qualitatively, but can be understood well, with the Rydberg gas model described in papers II and III (R. S. Mason, and R. S. Mason and P. Douglas, PCCP, 2010, DOI: 10.1039/b918081h and b918083d) over a wide range of probe bias voltages. The full cycle of behavior is then described for the development of a true secondary discharge within the downstream plasma.

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Rydberg gas theory of a glow discharge plasma: III. Formation, occupied state distributions, free energy, and kinetic control

Mason

Douglas

2010

Phys. Chem. Chem. Phys.

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It has been suggested that Rydberg gas atoms are involved in conducting electricity through a steady state flowing afterglow (FAG) discharge plasma (R. S. Mason, D. J. Mitchell and P. M. Dickinson, Phys. Chem. Chem. Phys., 2010, DOI: ). From known properties of Rydberg atoms, a statistical model is developed here to find the distribution of levels (principal quantum number n) occupied in such a hypothetical Rydberg gas. It behaves non-ideally at positive column plasma densities, predicting 30 < n < 150, peaking at n approximately = 85. These values depend on assumptions concerning the power of n dependency of 'pressure ionization' and the free charge density. The occupied states are very long-lived and almost completely separated from the low n states by the low probability of intermediate levels. The effects of Rydberg gas (N(R)) and free charge densities are examined. The gas can exist in a deep free energy well (> 120 kJ mol(-1) below ionisation level when 10(10) < or = N(R) < or = 10(11) atoms cm(-3)) but this is approximately 11 kJ mol(-1) higher than that of the equivalent free ion-electron gas; therefore if it exists in preference to the classical form of the plasma, it is controlled by kinetic factors. A mechanism is suggested by which this could occur. Thus, whilst ionization by high energy electron impact occurs at the Cathode Fall-Negative Glow (NG) boundary as usual, excitation of Rydberg atoms becomes more probable, by electrons slowed by collision and deceleration at the opposite NG-Positive Column (PC) plasma boundary. The atoms become stabilized after passing into the PC, by collisionally induced (nlm) mixing of states and the removal of free charge by charge transfer (and hence the passage of electric current through the Rydberg gas). The coupling of Rydberg states with the ionization continuum is poor; therefore, if the rate of their charge transfer is greater than that of their ionization, the Rydberg gas will remain relatively charge free and hence stable when it is conducting a current. When applied to the FAG plasma, the model provides a self-consistent interpretive framework for all its electrical, mass spectrometric and chemical behaviour. The effect on the optical spectroscopy of these plasmas is considered briefly.

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Rydberg gas theory of a glow discharge plasma: II. Electrode kinetics (probe theory) and the thermal rate constant for Symmetrical charge transfer involving Rydberg atoms of Ar

Cited by 3 publications

References 10 publications

Glow Discharge Mass Spectrometry

Glow Discharge Mass Spectrometry

Rydberg gas theory of a glow discharge plasma: I. Application to the electrical behaviour of a fast flowing glow discharge plasma

Rydberg gas theory of a glow discharge plasma: III. Formation, occupied state distributions, free energy, and kinetic control

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