Thermodynamic model for electron emission and negative- and positive-ion formation in keV molecular collisions

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Abstract

A statistical-type model is developed to describe the ion production and electron emission in collisions of (molecular) ions with atoms. The model is based on the Boltzmann population of the bound electronic energy levels of the quasimolecule formed in the collision and the discretized continuum. The discretization of the continuum is implemented by a free-electron gas in a box model assuming an effective square potential of the quasimolecule. The temperature of the electron gas is calculated by taking into account a thermodynamically adiabatic process due to the change of the effective volume of the quasimolecule as the system evolves. The system may undergo a transition with a small probability from the discretized continuum to the states of the complementary continuum. It is assumed that these states are decoupled from the thermodynamic time development. The decoupled states overwhelmingly determine the yield of the asymptotically observed fragment ions. The main motivation of this work is to describe the recently observed H- ion production in OH++Ar collisions. The obtained differential cross sections for H- formation, cation production, and electron emission are close to the experimental ones. Calculations for the atomic systems O++Ar and H++Ar are also in reasonable agreement with the experiments indicating that the model can be applied to a wide class of collisions.

Original languageEnglish
Article number022707
JournalPhysical Review A - Atomic, Molecular, and Optical Physics
Volume94
Issue number2
DOIs
Publication statusPublished - Aug 15 2016

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molecular collisions
positive ions
negative ions
electron emission
continuums
thermodynamics
collisions
electron gas
ions
molecular ions
free electrons
boxes
energy levels
fragments
cations
cross sections
electronics
atoms
temperature

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

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title = "Thermodynamic model for electron emission and negative- and positive-ion formation in keV molecular collisions",
abstract = "A statistical-type model is developed to describe the ion production and electron emission in collisions of (molecular) ions with atoms. The model is based on the Boltzmann population of the bound electronic energy levels of the quasimolecule formed in the collision and the discretized continuum. The discretization of the continuum is implemented by a free-electron gas in a box model assuming an effective square potential of the quasimolecule. The temperature of the electron gas is calculated by taking into account a thermodynamically adiabatic process due to the change of the effective volume of the quasimolecule as the system evolves. The system may undergo a transition with a small probability from the discretized continuum to the states of the complementary continuum. It is assumed that these states are decoupled from the thermodynamic time development. The decoupled states overwhelmingly determine the yield of the asymptotically observed fragment ions. The main motivation of this work is to describe the recently observed H- ion production in OH++Ar collisions. The obtained differential cross sections for H- formation, cation production, and electron emission are close to the experimental ones. Calculations for the atomic systems O++Ar and H++Ar are also in reasonable agreement with the experiments indicating that the model can be applied to a wide class of collisions.",
author = "Z. Juh{\'a}sz",
year = "2016",
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N2 - A statistical-type model is developed to describe the ion production and electron emission in collisions of (molecular) ions with atoms. The model is based on the Boltzmann population of the bound electronic energy levels of the quasimolecule formed in the collision and the discretized continuum. The discretization of the continuum is implemented by a free-electron gas in a box model assuming an effective square potential of the quasimolecule. The temperature of the electron gas is calculated by taking into account a thermodynamically adiabatic process due to the change of the effective volume of the quasimolecule as the system evolves. The system may undergo a transition with a small probability from the discretized continuum to the states of the complementary continuum. It is assumed that these states are decoupled from the thermodynamic time development. The decoupled states overwhelmingly determine the yield of the asymptotically observed fragment ions. The main motivation of this work is to describe the recently observed H- ion production in OH++Ar collisions. The obtained differential cross sections for H- formation, cation production, and electron emission are close to the experimental ones. Calculations for the atomic systems O++Ar and H++Ar are also in reasonable agreement with the experiments indicating that the model can be applied to a wide class of collisions.

AB - A statistical-type model is developed to describe the ion production and electron emission in collisions of (molecular) ions with atoms. The model is based on the Boltzmann population of the bound electronic energy levels of the quasimolecule formed in the collision and the discretized continuum. The discretization of the continuum is implemented by a free-electron gas in a box model assuming an effective square potential of the quasimolecule. The temperature of the electron gas is calculated by taking into account a thermodynamically adiabatic process due to the change of the effective volume of the quasimolecule as the system evolves. The system may undergo a transition with a small probability from the discretized continuum to the states of the complementary continuum. It is assumed that these states are decoupled from the thermodynamic time development. The decoupled states overwhelmingly determine the yield of the asymptotically observed fragment ions. The main motivation of this work is to describe the recently observed H- ion production in OH++Ar collisions. The obtained differential cross sections for H- formation, cation production, and electron emission are close to the experimental ones. Calculations for the atomic systems O++Ar and H++Ar are also in reasonable agreement with the experiments indicating that the model can be applied to a wide class of collisions.

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