Cross Sections for Dissociative Ionization of Molecules by Electron Impact

Rapp, Donald; Englander‐Golden, Paula; Briglia, Donald D.

doi:10.1063/1.1695897

Cited by 349 publications

(96 citation statements)

References 12 publications

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“…According to the few existing measurements, the energy scale of this distribution is approximately 15 eV. Since the cross section for the dissociative ionization of molecular hydrogen by electrons contributes only to 6% of the ionization cross section (Rapp et al 1965), we neglect this process in the simulation.…”

Section: Molecular Hydrogenmentioning

confidence: 99%

The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

178

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Abstract. We reexamine in detail the various processes undergone by positrons in the interstellar medium (ISM) from their birth to their annihilation using the most recent results of positron interaction cross sections with atomic and molecular hydrogen, as well as helium. The positrons' lives are divided into two phases: the "in-flight" phase (between ≈1 MeV and tens of eV) and the thermal phase. The first phase is treated with a Monte Carlo simulation that allows us to determine the fraction of positrons that form positronium and annihilate as well as the characteristics of the annihilation emission as a function of the medium conditions. The second phase is treated with a binary reaction rate approach, with cross sections adopted from experimental measurement or theoretical calculations. An extensive search and update of the knowledge of positron processes was thus undertaken. New reaction rates and line widths have been obtained. We investigate the treatment of the complicated interactions between positrons and interstellar dust grains. Fully relevant data were not always available, but we were nonetheless able to reach satisfactory understanding of positron annihilation on grains, both qualitatively and quantitatively. All factors of the problem have been considered, including the grain size distribution and composition, the electric charge of the grains, the backscattering, positronium formation and ejection from the grain, the pick-off annihilation inside them and the partial destruction of dust in the hot regions of the ISM. New reaction rates and widths of the line resulting from the annihilation inside and outside of the grain have been obtained. The final results of our calculations (reaction rates and spectra) showed that dust is only important in the hot phase of the ISM, where it dominates all other processes. Combining the new calculations, we have constructed annihilation spectra for each phase of the ISM, considering various grain contents, as well as an overall combined spectrum for the ISM as a whole.

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Section: Molecular Hydrogenmentioning

confidence: 99%

The lives and deaths of positrons in the interstellar medium

Guessoum

Jean

Gillard

2005

A&A

178

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“…will be an essential source of odd nitrogen, whose cross sections have been measured by WINTERS (1966) andRAPP et al (1965). As seen in Fig.…”

Section: Odd Nitrogenmentioning

confidence: 98%

Odd nitrogen in the lower thermosphere under auroral perturbations.

Kondo

Ogawa

1976

J. geomagn. geoelec

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A one-dimensional photochemical-diffusive model, allowing the auroral precipitation to induce a temporal variation of the source terms for minor species, is constructed to simulate height distribution of minor constituents in the mesosphere and lower thermosphere in the polar region. The dissociation of molecular nitrogen by impacts of precipitating electrons, together with the production of neutral odd nitrogen through ionic reactions caused by auroral ionizations, plays an essential role in determining the distribution of neutral odd nitrogen (N and NO) densities. Temporal variations of the N and NO densities during the auroral perturbation are quite different with different values of the quantum yield of N(2D) in the dissociation of N2. Enhancement of the NO density to a value more than a factor 10 larger than the normal value is possible above the height of 100 km in an IBC III aurora, as far as>0.5.The atomic nitrogen density grows rapidly during the precipitation, and decreases through the reaction with NO as soon as the perturbation ends. Alternatively if <0.1, the N density would increase to be comparable with that of NO, resulting in the lower NO density. A large value of j(>0.5) is favored from the recent observations of NO which revealed a larger density of NO in the polar thermosphere than in the low and middle latitudes. The prolonged enhancement of the NO density may influence the electron density and the ionic composition in the ionospheric E region during a pause of the auroral precipitation. The N0+ density more abundant than the O2 density would be maintained throughout the day even under the condition of intermittent precipitations of auroral electrons.

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“…Let's point out that the fact of possible failure of burning of the gas discharge for high voltages was indicated in ref [49].…”

Section: The Upper Branch Of a Curve Of The Self-sustained Discharge mentioning

confidence: 99%

“…2-4) are based on data [8,[36][37][38][39][40][41][42]. Total cross-sections of an electron -a nitrogen molecule collision were collected from [43][44][45][46][47] and cross sections of nitrogen molecule ionization from [48][49][50][51]. The excitation of 10 the lowest electronic states (data of [52,53]) and the 8 lowest vibration levels ( [54,55]) of a nitrogen molecule were accounted (Fig.…”

Section: Used Modelsmentioning

confidence: 99%

Runaway of electrons in dense gases and mechanism of generation of high-power subnanosecond beams

Ткачев

Yakovlenko

2004

Open Physics

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New understanding of mechanism of the runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of the avalanche electron multiplication is valid even for the strong electric fields when the electron ionization friction on gas may be neglected. A non-local criterion for a runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage U cr on pd for a certain gas (p is a pressure, d is an interelectrode distance). This dependence subdivides a plane (U cr , pd ) onto the area of the efficient electron multiplication and the area where the electrons leave the gas gap without multiplication. On the basis of this dependence analogs of Paschen's curves are constructed, which contain an additional new upper branch. This brunch demarcates the area of discharge and the area of e-beam. The mechanism of the formation of the recently created atmospheric pressure subnanosecond e-beams is discussed. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches to the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of the runaway electrons generation. The role of the discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as a propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.

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Cross Sections for Dissociative Ionization of Molecules by Electron Impact

Cited by 349 publications

References 12 publications

The lives and deaths of positrons in the interstellar medium

The lives and deaths of positrons in the interstellar medium

Odd nitrogen in the lower thermosphere under auroral perturbations.

Runaway of electrons in dense gases and mechanism of generation of high-power subnanosecond beams

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