Direct Observation of Distorted Wave Effects in Ethylene Using the (e,2e) Reaction

Abstract

We report here the direct measurements of electron momentum distributions for ethylene using the (e,2e) reaction at different impact energies from 400 to 2400 eV. The "turn up" effects in the (e,2e) cross sections of the 1b(3g) orbital compared with the plane-wave impulse approximation calculations were observed at low and high momentum regions, and such discrepancies become smaller with the increase of the impact electron energies. It is suggested that the observed discrepancies are due to the distorted-wave effects in molecules, while appropriate theoretical calculations using distorted waves in molecules could not be achieved until now.

Understanding energy loss in large-angle scattering of keV electrons from Ar and Ne

“…Expanding such theories to molecular targets is highly nontrivial, but desirable, e.g., for the interpretation of (e,2e) measurements of the electronic structure of molecules at intermediate energies [33], where distortion effects are known to influence the measured momentum densities.…”

Theoretical study of molecular vibrations in electron momentum spectroscopy experiments on furan: An analytical versus a molecular dynamical approach

“…This approximation implies that the kinetic energies of the incoming and two outgoing electrons are so high that their interactions with the molecular target or residual ion can be neglected. Breakdowns of the latter approximation have been almost systematically invoked [13][14][15][16][17][18][19] when facing strong discrepancies between theoretical and experimental momentum distributions, such as turn-ups of the recorded (e,2e) momentum densities at vanishing electron momenta. From EMS experiments upon atoms, such as Xe, 20,21 Zn, 22 and Cd, 23 it is known that orbitals exhibiting a d-type topology (i.e., two perpendicular nodal planes) are most commonly subject to distorted wave effects-an observation that has been experimentally verified in many situations.…”

An electron momentum spectroscopic study of naphthalene in gas phase

“…On the other hand, the discrepancy in the lower momentum region for both peaks was reduced as the impact energy increased from 600 eV to 1500 eV. Considering the similar phenomenon which has been observed in the atomic d orbitals and some molecular orbitals [24][25][26][27][28][29][30], such as ethylene [29] and oxygen [30] before, the most likely explanation is the distorted wave effects. The distorted wave effects will be reduced as the impact energies of electrons increase because the incoming electron and outgoing electrons will be less influenced by the residual ion's potential.…”