Inelastic scattering of fast electrons and the electron density of the scattering molecules

Theoretical and Experimental Chemistry -     

Elastic electron scattering by argon in the vicinity of the high-energy critical minimum

Differential cross sections (DCSs) for elastic electron scattering by argon in the vicinity of the high-energy critical minimum are presented. DCSs were measured as a function of both incident electron energy (90 –150 eV) and scattering angle (40°–126°). The absolute calibration was achieved via normalization to a single point. The positions of high angle DCS minimum versus incident electron energy were obtained. The experimentally obtained results are compared to the relativistic ab initio calculations based on the Dirac–Hartree–Fock method.     

Evaluation of cross sections for X-ray and high-energy electron scattering from molecular systems

An analytical and computationally efficient formalism for the evaluation of rotationally averaged cross sections for X-ray and high-energy electron scattering from molecular systems is given. Its application for both SCF and CI wave functions is discussed. © 1994 John Wiley & Sons, Inc.     

Elastic electron scattering from state-selected molecules

Electronically elastic, electron scattering cross sections are calculated for molecules in particular rotational states in order to establish the sensitivity of the scattering pattern to the quantum state. For the examples of diatomic molecules and symmetric tops considered here, the scattering pattern provides a unique fingerprint of the quantum state if one measures the scattered intensity for different orientations of the scattering vectors. The structure in the scattered intensity reflects the anisotropy of the square of the rotational wavefunction. Even for low angular momentum states which have diffuse rotational wavefunctions, very large differences in intensity are the result at certain scattering angles for states whose quantum numbers differ even by only one unit.     

Electron distribution in water by high-energy electron scattering

The differential cross-sections for high-energy electrons scattered from water have been measured over a wide range of momentum transfers. The effect of chemical binding was seen from the comparison between the experiment and the calculation for an independent-atom model. The ab initio calculation using SCF MO was carried out with respect to the elastic scattering. It was in a good agreement with the experiment and thus a reliable electron distribution in water was obtained.     

Elastic cross sections for electron scattering from GeF4: predominance of atomic-F in the high-energy collision dynamics

We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF(4). The incident electron energy range was 3-200 eV, while the scattered electron angular range was typically 15°-150°. In addition, corresponding independent atom model (IAM) calculations, within the screened additivity rule (SCAR) formulation, were also performed. Those results, particularly for electron energies above about 10 eV, were found to be in good quantitative agreement with the present experimental data. Furthermore, we compare our GeF(4) elastic DCSs to similar data for scattering from CF(4) and SiF(4). All these three species possess T(d) symmetry, and at each specific energy considered above about 50 eV their DCSs are observed to be almost identical. These indistinguishable features suggest that high-energy elastic scattering from these targets is virtually dominated by the atomic-F species of the molecules. Finally, estimates for the measured GeF(4) elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values.     

Elastic scattering of low and intermediate-energy electrons by Kr and Xe atoms

The many-body correlation forces, which act between the impinging electron and the bound electrons of the two heaviest rare gas atoms, are treated here using a newly developed correlation-polarisation potential that originates from the calculation of correlation energies in electronic bound-states of atoms and molecules. The new formulation of such forces, already tested by us for the lighter atomic targets, is particularly effective for the present systems and can be implemented very easily even for heavy atomic targets. The calculations reported in this paper show clearly that very good accord is obtained with more sophisticated theoretical treatments and with several experimental data on integral cross sections, momentum transfer cross sections and angular distributions.Von Humboldt — Prize Awardee 1992     

Small-Angle electron scattering and electron density in carbon dioxide

The total (elastic and inelastic) intensity of electrons scattered by CO₂ was measured in the s range of 1 to 12 Å^?1 and compared with the theoretical intensity calculated from the Hartree-Fock molecular wave function and those calculated for the independent-atom-model (IAM ) molecule. In the range of s ? 4 Å^?1 the electron correlation effect on the total scattered intensity was found to be represented by that for the IAM molecule.     

Elastic electron scattering by C2F4

Recent measurements [R. Panajotovic, M. Jelisavcic, R. Kajita, T. Tanaka, M. Kitajima, H. Cho, H. Tanaka, and S. J. Buckman, J. Chem. Phys. 121, 4559 (2004)] and calculations [C. Trevisan, A. E. Orel, and T. N. Rescigno, Phys. Rev. A 70, 012704 (2004)] of the elastic electron cross section for C(2)F(4) differ materially from our earlier calculations [C. Winstead and V. McKoy, J. Chem. Phys. 116, 1380 (2002)]. Some of the differences are readily attributed to approximations made in our computations, but an overall difference in cross section magnitude above ca. 10 eV was surprising. Here we report a reexamination of the electron-C(2)F(4) elastic cross section. After eliminating or minimizing various possible sources of error, we continue to predict a substantially larger cross section at higher energies.     

Elastic electron scattering cross sections of oriented and aligned molecules

Elastic differential electron scattering cross sections of oriented methyl iodide are calculated using the independent atom model. Results are presented for two specific orientations of the ICH₃ molecule for the purpose of comparison with the fictitious molecule IC, similarly oriented, at electron energies of 600 eV and 40 keV. Cross sections are also calculated for IC with a large angular momentum. In a comparison of the results for different orientations of the angular momentum vector, including random orientation, large differences between the cross sections are evident. This sensitivity to the plane of rotation of the molecule suggests the possibility of determining the degree of alignment of the angular momenta of a beam of such molecules by electron diffraction.     

Chemical interpretation of molecular electron density distributions

In this study, the two small molecules HS(CH)(CH(2)), 1, and F(CH)(4)F, 2, are presented, which yield different chemical interpretations when one and the same density is interpreted either by means of Natural Bond Orbital and subsequent Natural Resonance Theory application or by the Quantum Theory of Atoms In Molecules. The first exhibits a S-C bond in the orbital based approach, whereas the density based Quantum Theory of Atoms In Molecules detects no corresponding bond. In F(CH)(4)F a F...F bond is detected in the density based approach, whereas in the orbital based approach no corresponding bond is found. Geometrical reasons for the presence of unexpected and the absence of expected bond critical points are discussed.     

Elastic scattering of electrons by H2 in the born approximation

This paper presents accurate computation of the differential cross sections for the elastic and vibrational excitation of ground state H₂ by fast electrons. The electronic matrix elements are evaluated at 20 internuclear separations and proper averaging over vibrational wavefunctions is carried out. The comparison to experiment yields excellent agreement. Different computational procedures appropriate for low and moderate values of momentum transfer are compared.     

Coupling of the processes of dissociative recombination and scattering of slow electrons by molecular ions

A theory of dissociative recombination has been developed which makes possible an investigation of this process in connection with the problem of scattering of slow electrons by molecular ions. The simultaneous influence of direct (non-resonance) interaction and inhomogeneity of the electron continuum (due to the multichannel character of electron motion in the field of a molecular ion) is taken into account. The results obtained complement the resonance configuration interaction theory based on the Bardsley method and are important for interpreting the experimental data.     

A molecular connectivity study of electron density in alkanes

Molecular connectivity indices have been developed which characterize contributions of neighboring atoms to the CNDO/2 calculated electronic charge of a carbon atom. An analysis of these indices reveals their ability to predict this charge to 0.001 electron.