Dynamics of electron impact ionization of the outer and inner valence (1t₂and 2a₁) molecular orbitals of CH₄at intermediate and large ion recoil momentum

Abstract

The triply differential cross section has been measured for electron-impact ionization of the outer valence 1t2 and the inner valence 2a1 orbitals of methane using the (e,2e) technique with coplanar asymmetric kinematics. The measurements are performed at scattered electron energy of 500 eV, ejected electron energy of 12, 37 and 74 eV and for scattering angle of the fast outgoing electron of 6°. This kinematics is characterized by a target ion recoil momentum ranging from moderate (0.25 au) to very large (3.2 au) values. The results are compared with theoretical cross sections calculated using the 1CW and the BBK models recently extended to molecules. The experimental cross sections exhibit a very large recoil scattering, especially for the inner 2a1 molecular orbital, which is not predicted by the theory. The differences between experiment and theory are attributed to the very strong scattering from the ion, not properly accounted for by theory. This indicates the need for further theoretical developments as well as experimental investigations in order to correctly model the process of molecular ionization.

Experimental and theoretical investigation of the triple differential cross section for electron impact ionization of pyrimidine molecules

“…Interestingly, the HOMO binary peak here also appears quite narrow. This is in contrast to previous dynamical (e, 2e) studies on molecules, including for tetrahydrofuran, 17 formic acid, 16 water, 42 nitrogen, 43 and methane, 14 under similar kinematics in which very broad binary peaks have been observed for ionization of the HOMO.…”

“…Indeed, while there has been an increased interest in these studies over the last decade, both theoretical and experimental studies have mostly been limited to smaller targets. Recently, molecules including methane 14,15 and formic acid 16 have been investigated. Studies concerning larger molecules such as component molecules of DNA and RNA are rare, and include tetrahydrofuran 17 and theoretical studies on thymine.…”

Dynamical (e,2e) studies of tetrahydrofurfuryl alcohol

“…Comparably broad binary peaks have also been observed in experimental studies for molecules including water, 57 formic acid, 52 methane, 58 and nitrogen 59 under similar kinematics. Broad binary peaks were also observed for TDCS measurements of the HOMO of THF.…”

Triply Differential Ionization Cross Sections of atomic and molecular targets by single electron impact

“…In the work of El Mir et al these data were compared to analytical cross sections calculated within the FBA using the one coulomb wave model for the ejected electron with Slater-type wave functions developed according to the approach proposed by Moccia [14]. They also presented theoretical results using a distorted wave to describe the ejected electron and results calculated with the Brauner-Briggs-Klar model (BBK) [15]. The FBA results also underestimated the recoil peak but predicted a better binary to recoil amplitude ratio than the other models for the 3a 1 and 1e 1 orbitals.…”