Jon Siegel

Spectral variation of fixed‐molecule photoelectron angular distributions

We have computed the angular distribution of electrons ejected by electric‐dipole interaction from the K shells of CO and N2 molecules held fixed in space, e.g., by adsorption onto a surface. The predicted distributions are very rich in structure, manifesting directly the spectral variation of the orbital momentum composition of the photocurrent. Experimental determination of such distributions will provide a sensitive, detailed probe of molecular photoionization dynamics.

Shape resonances in e–SF6 scattering

Elastic scattering cross sections for e‐SF6 are calculated. The spectrum exhibits resonances of ag, t1u, t2g and eg symmetries between 0 and 40 eV.(AIP)

Elastic electron scattering by CO2, OCS, and CS2 from 0 to 100 eV

The integrated elastic electron scattering cross sections for CO2, OCS, and CS2 were calculated from 0 to 100 eV using the continuum multiple‐scattering model with the Hara exchange approximation. For each molecule, a strong π‐type shape resonance occurs between ∼1–4 eV, followed by multiple, weakly resonant features at higher kinetic energy. The latter are only marginally observable in the integrated cross section, but, in some cases, should be clearly observable in vibrational excitation spectra. Agreement with available experimental information is good for all three cases, except for a gross underestimation of the background (nonresonant) scattering cross section in OCS resulting from our omission of dipole scattering in this work.

Continuum and bound molecular electronic wavefunctions for generalized multiple‐scattering potentials

Existing multiple‐scattering treatments of bound and continuum electronic states of molecules are restricted to monopole potentials in the various spherical regions. We extend the treatment within these regions to a general potential. The corresponding multiple‐scattering equations should facilitate accurate treatment of, e.g., effects of the buildup of charge between atomic centers due to bonding, of the dipole character of polar molecules, and of external fields.

Effects of long- and short-range forces in e-CsCl scattering

The authors report hybrid calculations for elastic electron scattering from the highly polar molecule CsCl, which establish the origin of the shoulder at 30 degrees recently observed in the differential cross section at 20 eV. Their method incorporates dynamic effects of both dipole scattering at intermediate and long range (important at small angles theta ), and core scattering (important, typically, for larger angles). The shoulder, in spite of its location at small theta , is demonstrated conclusively to be a core defect.

Differential cross sections for e-LiF scattering

Differential cross sections are calculated for e-LiF scattering from 1 to 20 eV using a three-part hybrid method in which low-l partial waves are calculated using the multiple-scattering method, intermediate-l partial waves are calculated using the closed-form point dipole method and high-l waves are obtained using the first Born approximation. Good agreement between theory and experiment at 5.44 and 20 eV confirms the suitability of both the three-part hybrid approach and of the three separate approximations used therein. The differential cross section spectrum is dominated by dipole scattering at small angles, but clearly shows the influence of the molecular core at intermediate and large angles.

Electron scattering from HCN

The hybrid model of electron-polar molecule scattering has been used to calculate scattering of electrons from first-row diatomic molecules (LiF); large, strongly polar systems (CsCl); and systems showing pronounced vibrational effects (HCl, DCl). Initial results are reported for the extension to HCN, the first calculation on a polyatomic molecule and the first such calculation on a strongly polar system expected to display a characteristic shape resonance within a few eV of threshold. (GHT)

Closure formula for vibrational excitation in electron-polar molecule scattering

Application of the closure formula to electron-dipolar molecule scattering is straightforward if the nuclei are frozen at R = Re. Here it is applied to vibrationally inelastic scattering, focusing particularly on the R dependence of exact and Born approximation T matrix elements. This R-dependence must be the same for the two levels of approximation if the closure formula is to be applied.

Electron scattering from CsCl

A spectral study of electron-molecule scattering on cesium chloride is reported. A hybrid method of calculating the core potential is presented. At 5 and 20 eV, differential cross sections are compared between calculated and experimental with good agreement. (GHT)

Vibrational excitation in electron-DCl scattering

A preliminary report is given of the results of fixed-nuclei and adiabatic calculations of the e-HCl and e-DCl electron-molecule scattering systems. The calculations are performed in the rotational and vibrational adiabatic approximation, and the use of DCl rather than HCl allows calculation to substantially lower energy. (GHT)