Activation Energy for the Three-Body Reaction of Helium Triplet Atom with Normal Helium

Ludlum, Kenneth H.; Larson, Lewis P.; Caffrey, James M.

doi:10.1063/1.1840361

Cited by 21 publications

(6 citation statements)

References 12 publications

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“…In the case of the ( ) He 2 S 3 state, the potential energy curve for the He 2 electronic state is also very slightly repulsive (with a barrier of only 0.06 eV [47]) which makes the three body association process…”

Section: Formation Of Helium Molecules By Association Processesmentioning

confidence: 99%

Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

Carbone

Schregel

Czarnetzki

2016

Plasma Sources Sci. Technol.

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In this paper, we discuss the experimental results presented in Schregel et al (2016 Plasma Sources Sci. Technol. 25 054003) on a high pressure micro-discharge operated in helium and driven by nanosecond voltage pulses. A simple global plasma chemistry model is developed to describe the ions, excited atomic and molecular species dynamics in the ignition and early afterglow regimes. The existing experimental data on high pressure helium kinetics is reviewed and critically discussed. It is highlighted that several inconsistencies in the branching ratio of neutral assisted associative and dissociative processes currently exist in the literature and need further clarification.The model allows to pinpoint the mechanisms responsible for the large amounts of Rydberg molecules produced in the discharge and for the helium triplet metastable state in the afterglow. The main losses of electrons are also identified. The fast quenching of excited He (n > 3) states appears to be a significant source of Rydberg molecules which has been previously neglected. The plasma model finally draws a simplified, but still accurate description of high pressure helium discharges based on available experimental data for ion and neutral helium species.

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Section: Formation Of Helium Molecules By Association Processesmentioning

confidence: 99%

Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

Carbone

Schregel

Czarnetzki

2016

Plasma Sources Sci. Technol.

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“…The reason why k R1 has a strong correlation with T g and decreases at low T g is that there is a small hump in the potential energy in the collision between He m and ground He atoms, 36) forming the activation energy (∼0.067 eV), which is in a similar range to the thermal energy. 37) For the Penning reactions (R2-R4), we assume that the dependence of the reaction rate coefficients (k) on the gas temperature varies with ffiffiffiffiffi T g p , only considering the change in collision frequency. 30) The listed reactions are representatives of He m quench processes; however, note that the actual reaction system in the discharge in He with air impurities is more complex than the listed reactions, as suggested in the literature, for instance Refs.…”

Section: Discussionmentioning

confidence: 99%

Laser absorption spectroscopy diagnostics of helium metastable atoms generated in dielectric barrier discharge cryoplasmas

Urabe

Muneoka

Stauss

et al. 2015

Jpn. J. Appl. Phys.

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Cryoplasmas, which are plasmas whose gas temperatures are below room temperature (RT), have shown dynamic changes in their physical and chemical characteristics when the gas temperature in the plasmas (T gp ) was decreased from RT. In this study, we measured the temporal behavior of helium metastable (He m ) atoms generated in a parallel-plate dielectric barrier discharge at ambient gas temperatures (T ga ) of 300, 100, and 14 K and with a gas density similar to atmospheric conditions by laser absorption spectroscopy. The increments of T gp to T ga were less than 20 K. We found from the results that the He m lifetime and maximum density become longer and larger over one order of magnitude for lower T ga . The reasons for the long He m lifetime at low T ga are decreases in the rate coefficients of three-body He m quenching reactions and in the amounts of molecular impurities with boiling points higher than that of He.

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“…The temperature dependence of reaction (2.1) has been discussed in Sec. II A. Ludlum, Larson, and Caffrey [15], determined the rate of reaction (2.9) at 77 K, and Fugol, Grigoraschenko, and Myshkis [52], made determinations of this rate at 300, 120, 80, and 10 K. Compared to the rate of reaction (2.1), the rate of reactive collision between S atoms is only moderately temperature dependent; Fugol's measurement at 300 K was only about twice that determined at 10 K. Determinations of the rate of S diffusion [53] have been made as a function of temperature to 4.2 K. Because of the repulsive barrier in the a X"+-state potential curve, the diffusion rate decreases steadily with temperature.…”

Section: B Rovibrational Relaxation Of the Metastable He2 Moleculesmentioning

confidence: 98%

“…Because the a X"+-state potential curve exhibits a repulsive hump between the attractive well and the 1S2s S -1s 'S separated-atom asymptote, the rate associated with this reaction has a strong temperature dependence. Measurements of this rate at various temperatures were made by Phelps and Molnar [14] and by Ludlum, Larson, and Caffrey [15]. In the most recent study [16], measurements were taken between 65 and 700 K. Below The first process listed is a simple three-body conversion of the atomic ion to the diatomic molecular ion.…”

Section: Previous Work On the Kinetics Of Helium Plasmasmentioning

confidence: 99%

Reaction dynamics of metastable helium molecules and atoms near 4.2 K

1993

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Infrared absorption spectra from metastable helium atoms (2s S, 2s 'S) and molecules (a X"+) were previously acquired by irradiating dense helium gas near 4.2 K with a pulsed proton beam [R. L. Brooks, J. L. Hunt, and D. W. Tokaryk, J. Chem. Phys. 91, 7408 (1989)]. The molecular spectrum was unusual because the observed rovibrational distribution within the a X"+ state was far from thermal equilibrium.Three different rovibrational groups were observed: (i) v =0, N=1 ("thermal" molecules); (ii) u =0, 9 «N «21 (rotationally excited molecules); and (iii) 10«v «12, N=1 (vibrationally excited molecules).In this work, the time evolutions of members of these three molecular populations were studied both during irradiation and in the subsequent afterglow. In addition, the evolution of the 2s S -2p 'P atomic line was investigated. This study quantitatively explores the reaction dynamics of the metastable molecule in the gas phase near 4.2 K. Gas pressures between 100 and 750 Torr were used. Time-resolved data were taken with a transient-digitizer system and summed for several thousand cycles of the pulsed proton beam. The absorption measurements were converted to time-resolved number densities with the aid of theoretical transition moments. The analysis required that the data be fit to the solutions of sets of coupled differential equations with a nonlinear least-squares-fit routine. The results provide insight into the complicated reactions involved in generating the unusual molecular distribution and into the reactions between the metastable molecules, metastable atoms, and the background helium gas.PACS number(s): 34.50. Gb, 34.50.Lf, 82.20.Pm

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Activation Energy for the Three-Body Reaction of Helium Triplet Atom with Normal Helium

Abstract: Study of twobody and threebody channels for the reaction of metastable helium atoms with selected atomic and molecular species J. Chem. Phys. 88, 3061 (1988); 10.1063/1.453949Study of twobody and threebody channels for the reaction of metastable helium atoms with nitrogen

Cited by 21 publications

References 12 publications

Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

Ignition and afterglow dynamics of a high pressure nanosecond pulsed helium micro-discharge: II. Rydberg molecules kinetics

Laser absorption spectroscopy diagnostics of helium metastable atoms generated in dielectric barrier discharge cryoplasmas

Reaction dynamics of metastable helium molecules and atoms near 4.2 K

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