Ludwig Boesten

Elastic and vibrationally inelastic cross sections and energy loss spectra for electron collisions with GeH4

Absolute vibrationally elastic cross sections for e-GeH4 collisions have been determined for electrons of 1, 2, 2.5, 3, 5, 7.5, 10, 15, 20, 60 and 100 eV incidence energy over a scattering angular range of 10 degrees -130 degrees . The observed angular distributions correspond, at least qualitatively, to theoretical formulations using the continuum-multiple-scattering method, the parameter-free static-exchange-polarization approximation, and a multichannel Schwinger variational calculation. Vibrational excitation functions and the energy distribution of elastically scattered electrons reveal a shape resonance at about 2-2.5 eV. Calculations show that the resonance scattering state belongs to the t2 representation of the Td point group, which is also the representation of the lowest unoccupied molecular orbital (LUMO) of GeH4. Energy loss spectra recorded in the electronic threshold region of GeH4 reveal enhanced inelastic scattering at large angles in the loss range 7-9 eV characteristic of excitation to the lowest triplet state.

Elastic scattering and some vibrational excitation cross sections for electron collisions with Si2H6

Absolute elastic cross sections for e-disilane collisions have been measured by using incident kinetic energies of 2, 3, 4, 5, 7.5, 10, 15, 20, 40, and 100 eV and recorded over a scattering angular range of 10-130 degrees . These cross sections have been integrated by employing a nonlinear phase shift fitting procedure to generate a list of integral elastic and momentum transfer cross sections for the same energy range. The angular distributions have been found to agree reasonably well with a continuum multiple scattering calculation using only local potentials and also with a multichannel Schwinger variational calculation. Limited experiments on vibrationally inelastic scattering reveal the existence of a shape resonance with a peak at approximately 2 eV that is characteristic of trapping by a valence orbital with Si-H antibonding character analogous to that encountered in e-monosilane scattering.

Electron energy loss spectroscopy of disilane

Electron energy loss spectra of disilane have been recorded over an excitation energy range of 20 eV employing electrons of 20 and 200 eV incident energy for scattering angles of 0°–90°. Every transition detected except one appears at an energy consistent with the first observed members of Rydberg series converging to one of four possible ion states. The first two observed transitions belong to (2a1g)2→1,3(2a1g,4s) dipole forbidden channels appearing at excitation energies of ∼6.3 and 7.05 eV for the triplet and singlet, respectively. Evidence is presented for the identification of additional forbidden transitions as well as possible low‐lying valence transition.

Observation of the lowest triplet state in silane by electron energy loss spectroscopy

The electron energy loss spetra of silane was recorded at several impact energies and angles. It is concluded that the lowest triplet state of silane is formed from configuration mixing of the 4s Rydberg state with a valence state of the same symmetry.(AIP)

Crossed-Beam Experiment for the Scattering of Low Energy Electrons from Gas Phase C60

Elastic electron scattering spectra of C 60 in the vapor phase were recorded from 1 to 11.5 eV and scattering angles from 30° to 90° . Electron energy loss spectra are given for a loss from 1 to 55 eV at impact energies of 50 and 100 eV (5° ). They confirm the known optically allowed transitions and resolve the ≈6 eV π-electron plasmon-peak at least into four steps at 5.8, 6.1, 6.3, and 6.5 eV. A small peak of width 2 eV has been found at 28.3 eV, the position of the “σ+π-plasmon” in solid films. Vibrational excitations were recorded at 7 eV for angles from 20° to 60° with a resolution of 34 meV and show two peaks at 0.06 to 0.11 eV and at 0.15 to 0.20 eV both of which contain optically forbidden transitions. The elastic DCS at 7 eV and a scattering angle of 30° is estimated to be of order 5×10 -14 cm 2 /sr.