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

Abstract

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.

Distorted-wave Born Approximation for the Ionisation of Hydrogen by Electrons

“…Avaldi et al (1987) have used a combination of these methods, integrating the differential cross sections to obtain double differential cross sections for comparison with relative double differential cross sections measured as a function of momentum transfer and normalised by extrapolating to the optical limit. Lahmam-Bennani et al (1987) find very good agreement between the three methods. Ehrhardt et al (1985Ehrhardt et al ( , 1986, Klar et al (1987), open squares: experimental data of Lohmann et al (1984), solid curve: DWBA (this work), long dashes: coupled pseudostate method (Curran and Walters 1987), short dashes: calculation incorporating the exact three·body boundary condition (Brauner et al 1989).…”

“…Both depend to some extent on the validity of the first Born approximation for the double differential cross section. For example Lahmam-Bennani et al (1983) integrate the asymmetric differential cross sections over all directions of the slower electron to estimate the double differential cross section. This is normalised by comparison with measured double differential cross sections put on an absolute scale by using the Bethe sum rule (Lahmam-Bennani et al 1980).…”

“…For example Lahmam-Bennani et al (1983) integrate the asymmetric differential cross sections over all directions of the slower electron to estimate the double differential cross section. This is normalised by comparison with measured double differential cross sections put on an absolute scale by using the Bethe sum rule (Lahmam-Bennani et al 1980). The Bethe sum rule is valid if the first Born approximation describes the double differential cross section accurately enough.…”

Electron-impact core excitation ofSF6. II. Generalized oscillator strengths in the S 2pregion

“…Shell-specific Compton profiles can be derived from the GOS measurements [29][30][31].Bonham and Wellenstein [32] have shown how one can analyze the Compton profile in Bethe surfaces to determine the charge and momentum distributions of the valence-shell electron densities of atoms and molecules. Even though the potential of EELS to provide additional spectroscopic information has been known for years, there has been little examination of nondipole core-excited states and relatively few systematic measurements of the GOS for valence-shell [20,27,33 -40], and particularly inner-shell [1, 41 -45], excitation.…”

Scattering of high‐energy electrons and x‐rays from molecules: The 10‐electon series Ne, HF, H2O, NH3, and Ch4

“…However, in recent years a few groups have started measuring the absolute elastic and inelastic intensities separately. In this regard the work of Lahman-Bennani et al [3] is worth mentioning.…”