Charge-Exchange Cross Sections for Argon Ions in H2 and D2 below 1 keV

Amme, Robert C.; McIlwain, J. F.

doi:10.1063/1.1727741

Cited by 30 publications

(3 citation statements)

References 13 publications

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“…Except very near threshold our results for both Ar ϩ ϩH 2 and Ar ϩ ϩHD are nearly constant at 60 Å 2 whereas Chapman's values are somewhat smaller. Experimental values for the charge transfer cross sections [1][2][3]7,33,34 are much smaller than our values. This is not surprising, because it is now well known 35 that charge transfer at energies below Eϭ100 eV for a system like Ar ϩ ϩH 2 is primarily determined by the vibronic energy levels and Frank-Condon factors between the reactants and products and can only be properly calculated by treating the electronic and vibrational degrees of freedom quantum mechanically.…”

Section: Resultscontrasting

confidence: 69%

Theoretical study of the reactions of Ar++H2 and Ar++HD using the trajectory surface hopping method

Sizun¹,

Song

Gislason

1998

The Journal of Chemical Physics

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Trajectory surface hopping calculations have been carried out for collisions of Ar ϩ ϩH 2 and Ar ϩ ϩHD on three low-lying potential energy surfaces projected from the original six in the Kuntz and Roach diatomics in molecules surface for this system. The location and probability of hops between surfaces were determined using the new algorithm developed by Parlant and Gislason. In addition to the reactive channel and total charge transfer to H 2 ϩ and HD ϩ , dissociative channels to, for example, Ar ϩ ϩHϩH, and ArϩH ϩ ϩH have been studied. Particular attention was paid to the dissociative charge transfer isotope effect for the processes Ar ϩ ϩHD→ArϩH ϩ ϩD, or ArϩHϩD ϩ ; near threshold the D ϩ product is favored over H ϩ which we attribute to preferential dissociation of excited ArD ϩ products. This is the first theoretical study of these dissociation processes.

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Section: Resultscontrasting

confidence: 69%

Theoretical study of the reactions of Ar++H2 and Ar++HD using the trajectory surface hopping method

Sizun¹,

Song

Gislason

1998

The Journal of Chemical Physics

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“…where I is the measured signal, I 0 the un-attenuated intensity, n H 2 the density of molecular hydrogen, d s the sheath width, and s a the cross section for asymmetric charge exchange. Taking 28 d s E 2 cm and s a E 1.5 Â 10 À15 cm 2 , 44,48 the (I 0 /I) ratio is 1.78 for a pressure of 0.7 Pa and 4.20 for a pressure of 2 Pa. We can now use these values to correct the calculated Ar + signals. To a first approximation, the attenuation of Ar + ions is paralleled by a corresponding increase in the concentration of H 2 + that must also be taken into account.…”

Section: Resultsmentioning

confidence: 99%

On the ionic chemistry in DC cold plasmas of H2 with Ar

Méndez

Tanarro

Herrero

2010

Phys. Chem. Chem. Phys.

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An experimental diagnosis and kinetic modeling of the ionic chemistry in low pressure DC plasmas of H(2)/Ar has been carried out. The studies were performed at pressures of 2 Pa and 0.7 Pa, in a hollow-cathode discharge reactor, using as plasma precursor a H(2)/Ar mixture with 15% Ar content. Experimental measurements include distributions of ion fluxes to the cathode, as well as electronic temperatures and densities in the plasma glow. Besides the species resulting directly from electron impact ionization (H(+), H(2)(+), Ar(+) and Ar(2+)), the ions H(3)(+) and ArH(+) were found to be formed in large amounts through protonation reactions in the glow. In spite of the not too large variation in the pressure of the two plasmas, the differences in the ion distributions are worth mentioning. In the 2 Pa discharge (but not in the 0.7 Pa), H(3)(+) was the dominant ion and ArH(+) exceeded markedly the Ar(+) signal. On the other hand, the appearance of Ar(2+) in the two plasmas points at the relevance of high energy electrons. The experimental results can be accounted for by a simple kinetic model, after including corrections for the presence of a small fraction (<3%) of high energy (>50 eV) electrons and for the attenuation of the Ar(+) ions in the sheath through asymmetric charge exchange with H(2).

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“…Although, at the collision energies typical of the glow, the asymmetric charge exchange process R12 is unimportant as compared with reaction R13, the situation is inverted for the comparatively high collision energies of the sheath (up to 450 eV). Under this conditions, asymmetric charge exchange (R12), with a cross section σ ≈ 1.5 x 10 -15 cm 2 [29] dominates over protonation (R13) [30]. The decrease of the Ar + signal due to asymmetric charge exchange can be taken into account approximately by assuming a Lambert-Beer attenuation [22].…”

Section: H 2 /Ar Plasmasmentioning

confidence: 99%

Large effects of small pressure changes in the kinetics of low pressure glow discharges

Tanarro¹,

Herrero²

2011

Plasma Sources Sci. Technol.

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The effect of comparatively small pressure changes on the composition of low pressure hollow cathode DC discharges is investigated with a combination of experimental diagnostic techniques and simple models of the plasma kinetics. The plasma precursors considered are H 2 , Ar/H 2 mixtures, and air. In all cases, sudden characteristic composition changes are observed in the pressure interval between ≈ 0.5 and 3 Pa. Focusing the analysis on these distinctive changes has revealed most useful for the identification of key physicochemical processes in the various plasmas investigated. 1. Introduction Glow discharges are widely used in spectroscopic studies of excited levels or kinetics of highly reactive species (radicals and ions), which play a key role in the gas phase chemistry of combustion [1] or in remote regions of interstellar space [2, 3] and planetary ionospheres [4]. They find also widespread application in elemental analysis [5] and in a variety of technological processes [6], like sputtering [7], thin film processing [8, 9] plasma sterilization [10], and controlled fusion devices, where they are employed for wall conditioning and cleaning [11-14]. The chemical kinetics of the cold plasmas produced in glow discharges is ultimately determined by the disequilibrium between the high temperature of the light electrons (1-10 eV) and the much lower temperature (< 0.1 eV) of the heavy species (neutrals and ions). Glow discharges are stable over a pressure range determined by the suitable conditions for electron acceleration and multiplication in collisions with gas particles. The pressure of the gas determines the electron temperature and free charge density, the frequency of binary

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Charge-Exchange Cross Sections for Argon Ions in H2 and D2 below 1 keV

Cited by 30 publications

References 13 publications

Theoretical study of the reactions of Ar++H2 and Ar++HD using the trajectory surface hopping method

Theoretical study of the reactions of Ar++H2 and Ar++HD using the trajectory surface hopping method

On the ionic chemistry in DC cold plasmas of H2 with Ar

Large effects of small pressure changes in the kinetics of low pressure glow discharges

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