Intramolecular multiple scattering in electron diffraction from fluoro-methyl halides

Abstract

Abstract. Relative elastic differential cross sections for scattering of 1 keV electrons fiom CF3H, CF4, CF3C1, CH3F and CH3C1 molecules were measured for momentum transfer from 3 A -1 to 29 ~The oscillatory residuals remaining after substraction of the atomic scattering and the molecular interference contributions calculated in the independent atom model are ascribed to the influence of intramolecular multiple scattering. The data reflect the dominant contributions of the CF3-grou p and show larger oscillations than obtained from triple scattering calculations according to the method of Liu and Bonham using the second Born approximation.

Elastic Cross Sections for Electron Collisions with Molecules Relevant to Plasma Processing

“…In this regard we note the comprehensive data compilations from Christophorou et al 21 and Christophorou and Olthoff, 22 and the theoretical elastic scattering computations from Natalense et al, 23,24 Dimiz et al, 25 Morgan et al, 26 Varella et al, 27 and Iga et al 28 The work of Morgan et al also contained an electron-swarm analysis of the Schwinger multichannel computation results, while significant experimental results, from 1.5-30 eV, are contained in Varella et al 27 and, from 20-500 eV, in Iga et al 28 We also note additional experimental results from Meier et al 29 and Tanaka et al 30 In general, we find very good agreement between the data of Varella et al 27 and Tanaka et al, 30 when they are compared with the DCSs from Iga et al 28 at each common energy. As a consequence, our recommended data in Table 13 and Fig.…”

“…The original investigation into elastic electron scattering from CH 3 F came from Meier et al 29 However, as that was only a relative measurement at 1 keV, we need not consider it further. A preliminary study that concentrated on fluorination effects, but included elastic CH 3 F DCS at 1.5, 30, and 100 eV, was published by Tanaka et al 30 That measurement …”

Electron diffraction from oriented molecules:e?CH3Cl

“…The analogous observation was made for the case of CH3I [8], which has a similar molecular structure as CH3C1. Intramolecular multi-ple scattering could also influence the data, however, electron diffraction from unoriented CHaC1 showed that these effects are still small at our electron energies since the hydrogen atoms do not contribute strongly [10]. Since the atomic number is much lower for C1 than for iodine the IAM is expected to work better for the case of CH3C1.…”

“…Our experiment combines a supersonic molecular beam and an electron diffraction unit which can also be used for elastic electron scattering studies on unoriented molecules [10]. The apparatus consists of three differentially pumped vacuum chambers for beam generation, state selection and electron scattering.…”

“…of a seeded and pulsed beam which is presently not appropriate for the electron scattering unit. 3 and 4 with (da/df2) .... from [10] and by applying (1). The calculations predicted a similarly smooth increase of the beam intensity as a function of the hexapole voltage as observed in the experiment.…”