Elastic electron scattering from methane at high momentum transfer

J. Phys. B: At. Mol. Opt. Phys.

Went

2009

Self Cite

In high-momentum transfer electron scattering experiments the 'elastic signal' is separated into different components, depending on the mass of the scatterer due to the recoil effect. Here, we compare the peak positions and shapes obtained from H 2 , D 2 and HD with theory developed for neutron scattering experiments at similar momentum transfer. The hydrogen peak width increases with increasing momentum transfer. The observed width is in line with the vibrational properties of H 2 . The line shape of the elastic peak is also studied for HD and D 2 molecules. The H peak of HD is broader than the H peak of H 2 , and the D peak of D 2 is broader than the D peak of HD. We also investigate elastic scattering at high-momentum transfer of gas mixtures containing hydrogen and either heavy (Xe) or light (He) noble gases. Changing the energy of the incoming beam changes for the Xe/H 2 gas mixture the ratio of the Xe to H 2 signal in a dramatic way, but for the He/H 2 mixture the intensity ratio is constant. The energy dependence of the observed intensity ratio is in both cases accurately described by 'standard' differential elastic cross section calculations. Results are discussed in the context of a recent report of anomalies in electron scattering results of H 2 under similar experimental conditions and anomalous neutron scattering results of H 2 , D 2 mixtures and HD. An in-depth look at the peak shape of hydrogen reveals deviations from a simple Gaussian line shape which are interpreted to be, at least in part, a consequence of the bonding of the nucleus to a molecule.

“…The spectrometer is described in detail in [4], where it was used to study CH 4 . Currently, the gun has a BaO cathode to reduce the thermal spread of the beam.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Elastic electron scattering from hydrogen molecules at high-momentum transfer

J. Phys. B: At. Mol. Opt. Phys.

Went

2009

Self Cite

“…[42,43]. Two different spectrometers were employed, one for gas-phase measurements with E 0 between 600 eV and 6 keV and one for surface studies using energies up to 40 keV.…”

Section: A Experimental Proceduresmentioning

confidence: 99%

Exploring the Barkas effect with keV-electron scattering

Grande

2013

Phys. Rev. A

The energy loss of fast ions at close collision is mainly due to electron-ion collisions. The electrons are approximately stationary and they collide with a fast-moving ion. Here we study the same collision experimentally, in a reference system where the ions (or atoms) are stationary and interacting with keV electrons. Scattering cross sections under these conditions deviate from Rutherford, and we link these deviations, at higher energies, to the Z 3 contributions to the electronic stopping and the related Barkas effect and, at lower energies, also to quantum interference. The present measurements are well described by partial-wave calculations of the elastic cross section of electrons scattering from atoms. Encouraged by this agreement we use these calculations to estimate the Barkas factor for all elements and many energies. A universal curve for the Barkas factor due to close collisions is obtained for neutral projectiles and similar curves with smaller magnitude are found for ions.

The role of absorption in large-angle elastic scattering

Went

Journal of Electron Spectroscopy and Related Phenomena

2009

a b s t r a c tThe measurements of energy loss distributions obtained in electron scattering experiments at high momentum transfer are presented for Xe, Ar and methane. The spectra show a large variety of intensity distributions, clearly different from those obtained in measurements at the dipole limit. The fraction of the intensity present in the energy loss distribution compared to the elastic peak is significant, but is in line with the reduction of the elastic cross section due to absorption. It is argued that, if similar effects are present in the condensed phase, they should be dealt with in any quantitative analysis of electron transport in matter, as is often done using Monte Carlo simulations. This argument is worked out in some detail for Reflection Electron Energy Loss Spectroscopy.