Rate and mechanism of the thermal ionization of xenon

Johnston, Herrick L.; Kornegay, Wade M.

doi:10.1039/tf9615701563

Cited by 15 publications

(2 citation statements)

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“…The effect is a remarkable one since, e.g., BaO has a dissociation energy of 135 kcal/mole (ca.) while BaOH cannot have one (into Ba and OH) of much more than 60 kcal/mole (by analogy with the halides), which makes the ratio BaO: Ba: BaOH in a typical flame to be roughly 103 …”

Section: Electronic Excitation Of Metallic Compounds In Flames and C-mentioning

confidence: 99%

Excited Species in Flames

Sugden¹

1962

Annu. Rev. Phys. Chem.

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A finite resultant rate of chemical reaction in a system implies a lack of thermodynamic equilibrium, and therefore of a non-equilibrium distribution of the various chemical species over their accessible energy states. On a molecular-kinetic basis, the products of encounters in which chemical reac tion has taken place are endowed with at least the energy of activation of the reverse reaction, which must be shared for eqUilibrium to be attained. In a conventional "slow" reaction, such as the hydrogen-iodine reaction studied by Bodenstein, the rate of chemical reaction is slow compared with the attainment of thermal equilibrium between the various degrees of free dom concerned, and the only disequilibrium experimentally observable is that of the total concentrations of the reacting species. If, however, the rate of chemical reaction is sufficiently large, then departures from the Maxwell Boltzmann distribution of various species become evident. The extent of these depends on the relative "relaxation times" of chemical reaction and of exchange between the physical degrees of freedom-translational, rotational, vibrational, and electronic. This article will be concerned in the main with electronic disequilibrium. The development of new techniques for studying fast reactions, such as the shock tube, flash photolysis, molecular beams, and ultrasonics, has revolutionized our capabilities of observing systems with not only large chemical (Le. concentration) disequilibrium, but also physical disequilibrium. Along with these techniques go careful studies of the oldest known way of producing very rapid reactions-flames.The bulk of the work to be discussed here will relate to premixed flames, rather than diffusion flames, because the former give a more precise stratifi cation in space of chemical phenomena, particularly when set up on a burner that gives a flat flame rather than a conical one.

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Section: Electronic Excitation Of Metallic Compounds In Flames and C-mentioning

confidence: 99%

Excited Species in Flames

Sugden¹

1962

Annu. Rev. Phys. Chem.

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“…1 The examples given above are all electron-produciag, but many other reactions involving excited species (e.g., charge transfer, ion-molecule reactions, and de-excitation reactions) play significant roles in determining the electron production and recombination properties of the plasma.…”

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confidence: 99%

Research on Metastable Species in Atomic Molecular Beams Produced by Charge Transfer

Lorents¹,

Peterson²

1965

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BEST AVAILABLE COPY S TA NF OR I) R H S t A-R C 11 ! \ ^ t' I t U ,K c: A !, i ■ > ( Final Report RESEARCH ON METASTABLE SPECIES IN ATOMIC MOLECULAR BEAMS PRODUCED BY CHARGE TRANSFERMuch attention has been given to reactions among ground state atmospheric species and between atmospheric species and contaminants such as sodium which occur in the shock fronts and wake» of reentering vehicles.At the same time little consideration has been given to the effects of excited particles which obviously exist in great numbers in these gases.He cite, for example, three classes of reactions which are important in reentry-excited gases:1. N 2 + N 2 -N 2 + + N 2 + e 2. e + Na -N 2 + + 2eExcited N 2 is used as an example but these reactions will proceed with any long-lived excited species occurring in high temperature gases.Reactions of Class 1 have been shown to be an essential step in the initiation of ionization in shock waves. 1The examples given above are all electron-produciag, but many other reactions involving excited species (e.g., charge transfer, ion-molecule reactions, and de-excitation reactions) play significant roles in determining the electron production and recombination properties of the plasma.One of the main reasons excited state reactions have been neglected in models of shocks and wakes is that very little is known about them. We have also made some cursory measurements on tht reaction + + N 2 + Na -» N a + Na between 50 ard 450 eV. For the noble gas-alkali reactions we find cross sections that increase nonuniformly with increasing energy; their magnitudes range approximately from 0.5 to 1.5 x 10" l4 cffi 2 .For electron capture to the ground state, the reactions are highly nonresonant 10 eV); thus the ground state cross sections are probably smaller than 10~1 6 cm 2 . The magnitude of our cross sections is therefore indicative of electron capture mainly to excited states.in both He and Ar, short-lived states as well as metastable states will be populated, but at the present \:ime no knowledge concerning the relative populations of these states is available. Further reseprch is therefore needed to determine the fraction of the neutral beam remaining in metastable states after the short-lived states have had time to decay.However, it has been confirmed that conversion of ion beams to excited neutrals by this method can be done efficiently. With a properly designed system it should be possible to convert 30 to 50% of the ions in 9. beam to excited neutrals. 20 to 50% of which will remain in metastable states.This efficiency may be contrasted vith that of the electron bombardrent method which has laen used for many years to produce beams of excited particles at thermal velocities. The use of very intense electron beams to excite or ionize a large fraction of a neutral beam has been investigated by several people. 8A practical upper limit to the fraction of a thermal beam which can be ionized is about 17,; and since excitation cross sections are generally smaller than ionization cross sections, the upper...

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Ionization Relaxation in Slightly Impure Argon

Jones

McChesney

1966

Nature

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Rate and mechanism of the thermal ionization of xenon

Cited by 15 publications

References 5 publications

Excited Species in Flames

Excited Species in Flames

Research on Metastable Species in Atomic Molecular Beams Produced by Charge Transfer

Ionization Relaxation in Slightly Impure Argon

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