Low-energy elastic electron scattering from furan

Abstract

We report normalized experimental and theoretical differential cross sections for elastic electron scattering by C 4 H 4 O (furan) molecules from a collaborative project between several Brazilian theoretical groups and an experimental group at California State Fullerton, USA. The measurements are obtained by using the relative flow method with helium as the standard gas and a thin aperture target gas collimating source. The relative flow method is applied without the restriction imposed by the relative flow pressure condition on helium and the unknown gas. The experimental data were taken at incident electron energies of 1, 1.5, 1.73, 2, 2.7, 3, 5, 7, 10, 20, 30, and 50 eV and covered the angular range between 10 • and 130 • . The measurements verify observed π * shape resonances at 1.65 ± 0.05eV and 3.10 ± 0.05 eV scattering energies, in good agreement with the transmission electron data of Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004)]. Furthermore, the present results also indicated both resonances dominantly in the d-wave channel. The differential cross sections are integrated in the standard way to obtain integral elastic cross sections and momentum transfer cross sections. The calculations employed the Schwinger multichannel method with pseudopotentials and were performed in the static-exchange and in the static-exchange plus polarization approximations. The calculated integral and momentum transfer cross sections clearly revealed the presence of two shape resonances located at 1.95 and 3.56 eV and ascribed to the B 1 and A 2 symmetries of the C 2v point group, respectively, in very good agreement with the experimental findings. Overall agreement between theory and experiment regarding the differential, momentum transfer, and integral cross sections is very good, especially for energies below 10 eV.

Absolute cross sections for electron scattering from furan

“…The present absolute DCSs are compared at 50 eV with recently published experimental result by Khakoo et al 13 (it should be noted that the points below 15 • and above 130 • have been extrapolated by using the theory in Ref. 13) Although this DCS agrees very well in shape with the present experimental curve, it is somewhat lower in terms of the absolute scale.…”

“…Finally, we report tabulated results on experimental elastic DCSs in the energy range 50-300 eV, calculated ratios of vibrationally inelastic to elastic DCSs in the energy range 50-300 eV, and calculated integral elastic and total cross sections in the energy range from 10-10 000 eV. Also, both theoretical and experimental results for furan are compared to relevant recently published data 13,24 and previously reported results for the THF molecule 6 and discussed.…”

“…[33][34][35] In the present experiment, the ratio of the pressures behind the gas needle forming the molecular beam was adjusted to be around 2 (P Ar /P furan ), according to the available gas kinetic diameter for furan of 5.24 Å. 13 Also, the pressure of furan behind the needle was maintained below 0.2 mbars. Finally, it is worth pointing out that the absolute values of the cross sections did not depend crucially on the pressure ratios (within the uncertainties in the measured cross sections).…”

“…A considerable number of papers have been published concerning electron interaction with the furan molecule. Very recently, Khakoo et al 13 have reported experimental and theoretical DCSs for elastic electron scattering by furan at incident energies from 1 eV to 50 eV and in the angular range between 10 • and 130 • . Szmytkowski et al 24 reported absolute total cross sections, measured over energies from 0.6-400 eV using a linear electron transmission method; in the same paper the authors also reported calculated integral and ionization cross sections up to 4 keV, obtained by an additivity rule approximation and a binary-encounter-Bethe approach, respectively.…”

“…1) and belonging to C 2v point symmetry group. 12 Its structure can, therefore, be considered to be relevant as the simplest representative of the sugar unit in the DNA backbone, 13 similar to the tetrahydrofuran molecule (THF) which has been intensively investigated in recent years with this motivation. Particularly, theoretical and experimental absolute differential cross sections (DCSs) for elastic electron scattering by THF have been reported by several groups.…”