Marcel Rouault

Bethe surface and Compton profile of NH3 obtained by 35 keV electron impact

Complete inelastic electron impact spectra have been obtained for NH3 for a momentum transfer range from 0.4 to 12.5 a.u. using 35 keV electrons. These spectra were converted to relative generalized oscillator strengths (GOS), were placed onto an absolute scale by the Bethe sum rule, and higher order sum rules were used to test the accuracy of the GOS. The Compton profile (CP) of NH3 was determined from the GOS by means of the impulse approximation (IA) and it was found that the CP’s were asymmetric and shifted in respect to the free electron theoretical CP. This Compton defect was analyzed in detail and was shown to be due to the failure of the IA. The area under the CP is discussed in terms of the x‐ray incoherent scattering factor and experimental results for the valence, inner shell, and total CP’s are compared to several theoretical profiles.

Absolute triple differential cross sections for the 3p ionisation of argon by electron impact

The triple differential cross sections for electron impact ionisation of argon on its 3p orbital are investigated for a primary electron energy near 8 keV. In a coplanar coincidence experiment, both ionisation electrons are analysed with respect to their energy and scattering angles. As in previous low-energy measurements, two lobes are found in the angular distribution of the slow ejected electron. The data are made absolute to an accuracy of better than 10%. This is done at high energy and large momentum transfer, K, by normalising to the impulse approximation Compton profile and assuming a cylindrical symmetry of the data about K. At high momentum transfer where the collision may be considered as a binary electron-electron process, the Ar 3p electron momentum distribution is determined and found to be in very good agreement with the Fourier transform of the Hartree-Fock-Clementi wavefunction.

High energy elastic and inelastic electron scattering by the NH3 molecule‐binding effect

From the measurement of high energy elastic and inelastic electron scattering by the NH3 molecule we find that molecular elastic scattering calculation agrees with experiment, but the independent atom model for molecular inelastic scattering does not reproduce the experiment, even when electron correlations are taken into account. This means that the inelastic scattering by molecules is strongly affected by the rearrangement of the charge densities during the bond formation.

High energy elastic and inelastic electron scattering by the Ne and Ar atoms: Electron correlation effects

Elastic and inelastic differential cross sections (DCS) of high energy electrons (25 keV) scattered by neon and argon have been separately measured by totally independent methods. The effects of electronic correlations on the DCS and on the radial distribution functions D(R) and P(R) are deduced from experiment by comparison with theoretical Hartree–Fock values. An estimate of the correlation energy is also given. In the case of neon, the differences, with respect to Hartree–Fock, of the various contributions to atomic potential energy Δ Vne, Δ VeeCoul, and ΔVeeexch are calculated from experiment and compared to theoretical results.

The Compton profile of neon: Experimental study beyond the impulse approximation

High‐precision relative energy‐loss spectra of 25 keV electrons scattered from neon atoms are measured in the momentum transfer range 0.5 a.u.<K< 15 a.u. The corresponding generalized oscillator strengths are made absolute by use of the Bethe sum rule and then converted to Compton profiles (CP). These CP’s are shown to be K‐independent in the K ranges 5–7 and 13–15 a.u., where effective valence and total CP’s are respectively defined. Neither of these profiles is reproduced by the impulse approximation (IA) because of the existence of the so‐called Compton defect, i.e., a lack of symmetry in the intensity of the observed profile on the positive and negative q sides (q is the usual Compton parameter), and a shift of its maximum from the q=0 position predicted by the IA. Following a theoretical treatment proposed by Tavard and co‐workers for H and He, the experimental profiles are divided into their symmetrical (SCP) and antisymmetrical (ASCP) parts with respect to the q variable: the ASCP agrees with Tavar...

Asymmetry of the compton profile of ammonia

Abstract Using 35 keV electron impact spectroscopy, the asymmetry of the Compton profile of ammonia has been determined experimentally and the line shape studied as a function of momentum transfer K. Even at K = 12.5 a.u., the symmetry predicted by the impulse approximation does not hold. Preliminary results are also reported for He and N2.

Experimental determination of the effective contributions of the L+M and K electrons of argon to the Bethe sum rule

Energy loss spectra over a large energy loss range have been obtained for Ar using high energy electron impact spectroscopy. The sums of the generalized oscillator strengths for all possible excitation and ionization transitions have been determined separately for the L+M and K shell electrons relative to the Bethe sum rule for the whole atom. The effective number of electrons NK in the K shell of Ar was determined and found to be the same as theoretical predictions and experimental determinations for dipole oscillator strengths. (AIP)

High density molecular beam produced by a multichannel nozzle

A comparative study of gaseous beams used as targets in collision experiments is presented for two different kinds of nozzles. The angular spread of the beam at the nozzle output and the density distribution along the beam axis was measured by an electron diffraction method. The second step was to show the formation of clusters in the beam by increasing the pushing pressure. This was done by a measurement of the differential elastic cross section as a function of the scattering angle. The results show a better spatial localization and a higher density of the beam when obtained by the multichannel nozzle. Also the cluster formation in such a beam is less probable than in a free expansion beam.