Total Cross Sections for Ionization and Attachment in Gases by Electron Impact. I. Positive Ionization

Rapp, Donald; Englander‐Golden, Paula

doi:10.1063/1.1696957

Cited by 1,872 publications

(695 citation statements)

References 21 publications

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“…Figure 5 shows this comparison for non-dissociative ionization. The present cross section (continuous line) is in very good agreement with the experimental data [36,37,38,39]. The only theoretical data set available [19] is based on the Gryzinski theory combined with the Franck-Condon theory and perfectly reproduces the present data.…”

Section: Ionization Cross Sectionssupporting

confidence: 85%

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

Wünderlich

2011

Chemical Physics

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Ionization cross sections for the hydrogen molecule have been calculated by applying the classical Gryzinski theory combined with the Franck-Condon theory. It is shown that -if the reaction channels, Franck-Condon factors and Franck-Condon densities are taken into account properly -the calculated cross sections for ionization of the molecular ground state X 1 Σ + g (v ′ = 0) are in almost perfect agreement with the latest and most reliable experimental results. A comprehensive database is established which includes vibrationally resolved cross sections for non-dissociative and dissociative ionization of the molecular ground state as well as for the first five non-repulsive electronically excited states in the molecule.

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Section: Ionization Cross Sectionssupporting

confidence: 85%

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

Wünderlich

2011

Chemical Physics

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“…Cooling and heating mechanisms include -radiative cooling by H 2 lines excited by collisions with H, H 2 , He, and electrons (Le Bourlot et al 1999); -radiative cooling by CO, H 2 O, and 13 CO in the Large Velocity Gradient approximation (Neufeld & Kaufman 1993), and by OH and NH 3 in the low-density limit (Flower et al 1985); -atomic cooling by fine-structure and metastable lines of C, N, O, S, Si, C + , N + , O + , S + , Si + and Fe + (Giannini et al 2004); -inelastic scattering of electrons on H and H 2 (Aggarwal et al 1991;Hummer 1963;Rapp & Englander-Golden 1965); -energy released by collisional ionization and dissociation and exo/endo-thermicity of chemical reactions (Flower et al 1985); -energy heat/loss through thermalization with grains (Tielens & Hollenbach 1985); -ambipolar-diffusion heating by elastic scattering between the neutral fluid and charged ions and grains (Garcia et al 2001a, see Sect. 2.3); -ohmic heating arising from the drift between electrons and other fluids (Garcia et al 2001a, see Sect.…”

Section: Thermo-chemical Evolutionmentioning

confidence: 99%

Molecule survival in magnetized protostellar disk winds

Panoglou¹,

Cabrit²,

Forêts³

et al. 2012

A&A

108

144

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Context. Molecular counterparts to atomic jets have recently been detected within 1000 AU of young stars at early evolutionary stages. Reproducing these counterparts is an important new challenge for proposed ejection models. Aims. We explore whether molecules may survive in the magneto-hydrodynamic (MHD) disk wind solution currently invoked to reproduce the kinematics and tentative rotation signatures of atomic jets in T Tauri stars. Methods. The coupled ionization, chemical, and thermal evolution along dusty flow streamlines is computed for the prescribed MHD disk wind solution, using a method developed for magnetized shocks in the interstellar medium. Irradiation by (wind-attenuated) coronal X-rays and far-ultraviolet photons from accretion hot spots is included, with an approximate self-shielding of H 2 and CO. Disk accretion rates of 5 × 10 −6 , 10 −6 and 10 −7 M yr −1 are considered, representative of low-mass young protostars (so-called "Class 0"), evolved protostars ("Class I") and very active T Tauri stars ("Class II") respectively. Results. The disk wind has an "onion-like" thermo-chemical structure, with streamlines launched from larger radii having lower temperature and ionization, and higher H 2 abundance. The coupling between charged and neutral fluids is sufficient to eject molecules from the disk out to at least 9 AU. The launch radius beyond which most H 2 survives moves outward with evolutionary stage, from 0.2 AU (sublimation radius) in the Class 0 disk wind, to 1 AU in the Class I, and >1 AU in the Class II. In this molecular wind region, CO survives in the Class 0 but is significantly photodissociated in the Class I/II. Balance between ambipolar heating and molecular cooling establishes a moderate asymptotic temperature 700−3000 K, with cooler jets at earlier protostellar stages. As a result, endothermic formation of H 2 O is efficient, with abundances up to 10 −4 , while CH + and SH + can reach ≥10 −6 in the hotter and more ionised Class I/II winds. Conclusions. A centrifugal MHD disk wind launched from beyond 0.2−1 AU can produce molecular jets/winds up to speeds 100 km s −1 in young low-mass stars ranging from Class 0 to active Class II. The model predicts a high abundance ratio of H 2 to CO and an increase of molecular launch radius, temperature, and flow width as the source evolves, in promising agreement with current observed trends. Calculations of synthetic maps and line profiles in H 2 , CO and H 2 O will allow detailed tests of the model against observations.

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“…In Fig. 4, we compare available experimental data [14][15][16][17] with the BEB cross sections using the adiabatic and vertical IPs. It is clear that the agreement between theory and experiment between the threshold and TϽ100 eV is significantly improved by using the vertical IP.…”

Section: Methane (Ch 4 )mentioning

confidence: 99%

Electron-impact ionization cross sections of atmospheric molecules

Kim

Hwang

Weinberger

et al. 1997

The Journal of Chemical Physics

241

133

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A theoretical model for electron-impact total ionization cross sections, which has been found to be reliable for a wide range of molecules, is applied to molecules of interest to atmospheric science. The new theory, the binary-encounter-Bethe (BEB) model, combines the binaryencounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical data for the ground state of the target molecule, which are readily available from molecular structure codes. Total ionization cross sections of 11 molecules, CS, CS 2 , COS, CH 4 , H 2 S, NH 3 , NO 2 , N 2 O, O 3 , S 2 , and SO 2 , are presented for incident electron energies from threshold to 1 keV with an average accuracy of 15% or better at the cross section peak. We also found that the use of vertical ionization potentials (IPs) rather than adiabatic IPs for the lowest IPs significantly improves BEB cross sections between the threshold and cross section peak for molecules whose adiabatic and vertical IPs are different by ~1 eV or more (CH 4 and NH 3 ). The BEB cross sections are presented in a compact analytic form with a small number of constants, making the cross sections suitable for modeling applications. ©1997 American Institute of Physics. History:Received 20 August 1996; accepted 11 October 1996 A theoretical model for electron-impact total ionization cross sections, which has been found to be reliable for a wide range of molecules, is applied to molecules of interest to atmospheric science. The new theory, the binary-encounter-Bethe ͑BEB͒ model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical data for the ground state of the target molecule, which are readily available from molecular structure codes. Total ionization cross sections of 11 molecules, CS, CS 2 , COS, CH 4 , H 2 S, NH 3 , NO 2 , N 2 O, O 3 , S 2 , and SO 2 , are presented for incident electron energies from threshold to 1 keV with an average accuracy of 15% or better at the cross section peak. We also found that the use of vertical ionization potentials ͑IPs͒ rather than adiabatic IPs for the lowest IPs significantly improves BEB cross sections between the threshold and cross section peak for molecules whose adiabatic and vertical IPs are different by ϳ1 eV or more ͑CH 4 and NH 3 ). The BEB cross sections are presented in a compact analytic form with a small number of constants, making the cross sections suitable for modeling applications.

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Total Cross Sections for Ionization and Attachment in Gases by Electron Impact. I. Positive Ionization

Cited by 1,872 publications

References 21 publications

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule

Molecule survival in magnetized protostellar disk winds

Electron-impact ionization cross sections of atmospheric molecules

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