Dissociation and ionization of the methane molecule by nonrelativistic electrons including the near threshold region

Erwin, Daniel A.; Kunc, Joseph A.

doi:10.1063/1.2891694

Cited by 19 publications

(33 citation statements)

References 28 publications

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“…The CH cross section estimate is important to the role of CH in soot formation in the plasma combustion of CH 4 , as has been discussed in the past. 67 Presumably, our estimate of this branching is more reliable than the earlier estimates of Erwin and Kunc, 26,27 which were based on scaling arguments with no data for calibration at energies below 50 eV.…”

Section: Discussionmentioning

confidence: 41%

“…Methane is the primary hydrocarbon of interest in electron-induced fragmentation processes, both because of its intrinsic importance and because it serves as a model of more complex hydrocarbons. Numerous experimental and theoretical [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] studies have addressed methane-electron collisions. Most of these focused on elastic processes, reporting total 3, 6, 7, 11-16, 19, 29, 32, 33, 37 and elastic 1, 2, 4, 10, 15-17, 29, 30, 32, 33, 36 cross sections, so, the understanding of inelastic processes is far from complete.…”

Section: Introductionmentioning

confidence: 99%

“…Compared with the CH 3 formation yield measured in the two other laboratories, the CH 2 cross sections are much smaller in the threshold region. Erwin and Kunc 26,27 derived analytical expressions for the dissociative cross sections by using a scaling argument that relates the cross sections for the formation of neutral products to those for electron impact ionization that are better known. The data obtained from their formulae appear to be closer to the experimental results of Nakano et al in the low energy region, and to those of Motlagh and Moore, in the medium energy region.…”

Section: Introductionmentioning

confidence: 99%

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Modeling the electron-impact dissociation of methane

Ziółkowski

Vikár

Mayes

et al. 2012

The Journal of Chemical Physics

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The product yield of the electron-impact dissociation of methane has been studied with a combination of three theoretical methods: R-matrix theory to determine the electronically inelastic collisional excitation cross sections, high-level electronic structure methods to determine excited states energies and derivative couplings, and trajectory surface hopping (TSH) calculations to determine branching in the dissociation of the methane excited states to give CH(3), CH(2), and CH. The calculations involve the lowest 24 excited-state potential surfaces of methane, up to the ionization energy. According to the R-matrix calculations, electron impact preferentially produces triplet excited states, especially for electron kinetic energies close to the dissociation threshold. The potential surfaces of excited states are characterized by numerous avoided and real crossings such that the TSH calculations show rapid cascading down to the lowest excited singlet or triplet states, and then slower the dissociation of these lowest states. Product branching for electron-impact dissociation was therefore estimated by combining the electron-impact excitation cross sections with TSH product branching ratios that were obtained from the lowest singlet and triplet states, with the singlet dissociation giving a comparable formation of CH(2) and CH(3) while triplet dissociation gives CH(3) exclusively. The overall branching in electron-impact dissociation is dominated by CH(3) over CH(2). A small branching yield for CH is also predicted.

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Section: Discussionmentioning

confidence: 41%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling the electron-impact dissociation of methane

Ziółkowski

Vikár

Mayes

et al. 2012

The Journal of Chemical Physics

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“…102 There have been a number of studies on electron impact dissociation of methane. 46,63,72,[99][100][101][102][103][104][105][106][107][108][109][110][111][112] These include swarm studies, 45 1 also present a recommended value for electron impact dissociation stating that it is based on the electron beam measurements of Nakano et al 106 and Makochekanwa et al 112 These measurements are discussed further below, but the values recommended by Fuss et al appear to significantly higher than the published values given in the cited papers. These near-threshold results for electron collision energies up to 15 eV are summarized in Fig.…”

Section: Dissociation Cross Sectionmentioning

confidence: 99%

Cross Sections for Electron Collisions with Methane

Song¹,

Yoon²,

Cho

et al. 2015

Journal of Physical and Chemical Reference Data

131

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Cross section data are compiled from the literature for electron collisions with nitrogen trifluoride (NF 3) molecules. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer , excitations of rotational and vibrational states, dissociation, ionization, and dissociative attachment. For each of these processes, the recommended values of the cross sections are presented. The literature has been surveyed up to the end of 2016.

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“…The profiles of the photoelectron source function and the number densities of N 2 and CH 4 from INMS/CSN are used as input into the latter calculation, together with the cross sections and excitation/ ionization energies for electron-impact processes on N 2 (Majeed & Strickland 1997;Shemansky & Liu 2005;Itikawa 2006) and CH 4 (Erwin & Kunc 2005, 2008Liu & Shemansky 2006). …”

Section: Modelmentioning

confidence: 99%

Suprathermal Electrons in Titan’s Sunlit Ionosphere: Model–observation Comparisons

Vigren

Galand

Wellbrock

et al. 2016

ApJ

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The dayside ionosphere of the Saturnian satellite Titan is generated mainly from photoionization of N 2 and CH 4 . We compare model-derived suprathermal electron intensities with spectra measured by the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) in Titanʼs sunlit ionosphere (altitudes of 970-1250 km) focusing on the T40, T41, T42, and T48 Titan flybys by the Cassini spacecraft. The model accounts only for photoelectrons and associated secondary electrons, with a main input being the impinging solar EUV spectra as measured by the Thermosphere Ionosphere Mesosphere Energy and Dynamics/Solar EUV Experiment and extrapolated to Saturn. Associated electron-impact electron production rates have been derived from ambient number densities of N 2 and CH 4 (measured by the Ion Neutral Mass Spectrometer/Closed Source Neutral mode) and related energy-dependent electron-impact ionization cross sections. When integrating up to electron energies of 60 eV, covering the bulk of the photoelectrons, the model-based values exceed the observationally based values typically by factors of ∼3 ± 1. This finding is possibly related to current difficulties in accurately reproducing the observed electron number densities in Titanʼs dayside ionosphere. We compare the utilized dayside CAPS/ELS spectra with ones measured in Titanʼs nightside ionosphere during the T55-T59 flybys. The investigated nightside locations were associated with higher fluxes of high-energy (>100 eV) electrons than the dayside locations. As expected, for similar neutral number densities, electrons with energies <60 eV give a higher relative contribution to the total electron-impact ionization rates on the dayside (due to the contribution from photoelectrons) than on the nightside.

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Dissociation and ionization of the methane molecule by nonrelativistic electrons including the near threshold region

Cited by 19 publications

References 28 publications

Modeling the electron-impact dissociation of methane

Modeling the electron-impact dissociation of methane

Cross Sections for Electron Collisions with Methane

Suprathermal Electrons in Titan’s Sunlit Ionosphere: Model–observation Comparisons

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