Dynamic behavior of valence-shell excitations of atomic neon studied by high-resolution inelastic x-ray scattering

The high-resolution inelastic x-ray scattering has been applied to study the excitation mechanism of atomic neon. The different electric multipolar transitions of neon, i.e., the electric monopolar, dipolar, and quadrupolar ones, were clearly resolved, and their squared form factors were determined. It is found that for the monopolar and quadrupolar transitions the present inelastic x-ray scattering results are in agreement with the ones measured by high-energy electron scattering, while for the dipolar transition large discrepancies between the results measured by these two methods were observed. Such phenomena are well elucidated with the aid of the second-order Born approximation: Born amplitude of a transition near zero momentum transfer is the key factor which determines the behavior of the intramolecular multiple scattering in the high-energy electron scattering. It is revealed that the intramolecular multiple scattering in high-energy electron scattering must be considered for the dipole-allowed transition, while it is negligible for the dipole-forbidden ones.

Figure 1

A typical inelastic x-ray scattering spectrum of neon gas.

Figure 2

The squared form factors $\zeta (q,{\omega }_n)$ for the electric monopolar (a), dipolar (b), and quadrupolar (c) transitions of neon. Solid (blue) star: the present IXS results; open (pink) circle: the results of Cheng et al. [9] at the incident electron energy of 2.5 keV; solid (navy blue) line: the RPAE calculations [17]. The (red) triangle, (green) down-triangle, and (violet) square are the results of Suzuki et al. [33] measured at the incident electron energies of 300, 400, and 500 eV, respectively.

Figure 3

Sample Feynman diagrams of the dominant terms in $f_{B2}$ for the inelastic transition $({\mathbf{k}}_i,0)\to ({\mathbf{k}}_f,n)$ of neon.