Electron scattering fromH2O: Elastic scattering

Abstract

Differential cross sections for elastic electron scattering from gaseous water are reported. The measurements are obtained using the relative flow method with He as the standard gas and a thin collimating aperture source of gas instead of a conventional needle source. Differential cross sections were measured at incident energies of 1, 2, 4, 6, 8, 10, 15, 20, 30, 50, and 100 eV for scattering angles ranging from 5°to 130°and integrated over angles to obtain integral cross sections. Corresponding calculations of the differential cross section are carried out using the Schwinger multichannel method, employing extensive basis sets and considering polarization and dipole-scattering effects. Whereas excellent qualitative agreement with past measurements of differential cross sections is observed, our measurements are found to be consistently in significant quantitative disagreement with these measurements. The present calculations, on the other hand, generally agree in magnitude with previous results.

Low-energy electron scattering by tetrahydrofuran

“…• , similar to the range covered in an earlier work on water [31]. The uncertainties in the present DCS data (approximately 10% at most angles and energies) are taken to be the quadrature sum of the statistical uncertainty and reproducibility of scattered electron counts (1% to 4%), an uncertainty in the measured flow rates (5%, taken from the deviation in the gas pressure at the start and end of each measurement), and the reported uncertainty in the literature DCS values for helium (7%).…”

“…The electron detector (analyzer) was equipped with a five-element zoom lens plus a virtual aperture system that made it possible to detect low-energy electrons. The effusive target gas beam was formed by flowing gas through a thin aperture source 0.3 mm in diameter, described previously [31]. This aperture system was covered with soot from an acetylene flame to reduce secondary electrons and placed 6 mm below the axis of the electron beam, incorporated into a movable source arrangement [32].…”

“…Based on our flow-rate vs. drive-pressure analysis [31], the gas-kinetic molecular diameter of THF was determined to be 7.57 × 10 −8 cm, significantly larger than the molecular diameter quoted previously of 4.68 × 10 −8 cm [15,17]. Previously [33] we obtained a molecular diameter of 5.6 × 10 −8 cm for furan, and we note here that the dipole moment of THF, 1.63 D, is larger than that of furan, 0.66 D, by a factor of 2.5 [34]; moreover, THF is more massive (molecular weight 72.11 vs. 68.07 amu for furan) and has H atoms above and below the plane of the ring, while furan is planar.…”

Electron-impact vibrational excitation of tetrahydrofuran

“…The effusive gas beam target was formed by flowing THF gas through a thin aperture source 0.3 mm in diameter described previously [11]. This source was covered with carbon soot using a pure acetylene flame to reduce secondary electrons, and was placed 6 mm below the axis of the electron beam, incorporated into a movable source arrangement [12].…”

Low-energy elastic electron interactions with pyrimidine

“…Corresponding cross sections calculated using the ab initio Schwinger multichannel variational technique (SMC), and the IAM model are also reported. The Schwinger technique has been successfully applied in recent calculations of elastic scattering, electronic excitation, and dissociation in many complex polyatomic molecules of biological relevance, such as 3-hydroxytetrahydrofuran [12], uracil [13], water [14], and pyrazine [15]. The IAM model has been shown to be successful in describing the broad features of elastic scattering cross sections, for a number of complex polyatomic molecules, at energies above about 30 eV (e.g., [16,17]).…”