Electron detachment cross sections of ${\rm CH}_{4}^-$ colliding with O₂and N₂below 10 keV energies

Abstract

Negative methane is an interesting molecular anion from a fundamental point of view and also because it can be a source of thermal electrons in low temperature hydrocarbon plasma. Measurements of collisional electron detachment from methane anions colliding with O 2 and N 2 in the energy range of 0.3 to 10.0 keV are presented. Single electron detachment was measured with the signal grow-rate method and total electron detachment was measured with the beam attenuation technique. Both techniques were employed in order to study the process of electron detachment over the present energy range. The validity of the geometrical model is discussed.

Single electron capture cross sections for protons colliding with neon and methane targets: effects of the initial vibrational state of CH4

“…Both signals were counted with two identical CEMs, the count rates of which were maximized as a function of the voltage gain at each collision energy. With this technique, we have sustained that with the use of two identical CEMs, it is possible to achieve a combined counting efficiency close to unity [14]. A maximum error of 20% is quoted for the present data for the combined efficiency.…”

On the Accuracy of the Complete Basis Set Extrapolation for Anionic Systems: A Case Study of the Electron Affinity of Methane

“…From the experimental side work is currently in progress through a hybrid swarm/mass spectrometry technique to directly measure the electron affinity of metastable methane [8] with very high precision (c.a. 10 −2 eV).…”

Solving the CH4− Riddle: The Fundamental Role of Spin to Explain Metastable Anionic Methane

“…Electron-impact ionization processes have been thoroughly studied for gaseous methane over a very wide range of the density-normalized electric field strength up to 5×10 4 Td, also suggesting the presence of the methane anion [6]. In Townsend measurements at low E/N [8] large amounts of heavy negative ions were clearly observed so that the electron-attachment process in CH 4 is certain, thus providing irrefutable evidence of the presence of the methane anion [10]. From the theoretical side, the electron affinity (EA) was calculated as it is usually done [15] , i.e., as the difference between the energy of the doublet ground state 2 A 1 of the negative ion minus the energy of the singlet ground state 1 A 1 of neutral methane plus a free electron.…”

“…The CH 4 puzzle Methane has 10 electrons in a noble gas-like configuration so that electron capture by this very stable molecule is considered impossible. Nonetheless, electron attachment in methane has consistently been evidenced by several groups over five decades [1][2][3][4][5][6][7][8][9][10] though the true nature of this anionic species still remains unknown. Therefore, the elucidation of the origin and nature of anionic methane would be an important finding with implications on several fields, like our current understanding of atmospheric chemistry, hydrocarbon plasma, flame science, cluster science, space physics, planetary science and quantum chemistry.…”

“…Electron-impact ionization processes have been thoroughly studied for gaseous methane over a very wide range of the density-normalized electric field strength up to 5×10 4 Td, also suggesting the presence of the methane anion [6]. In Townsend measurements at low E/N [8] large amounts of heavy negative ions were clearly observed so that the electron-attachment process in CH 4 is certain, thus providing irrefutable evidence of the presence of the methane anion [10].…”