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Physical Review A

Rovibrational excitation of rare-gas dimers by electron impact

Eliton Popovicz Seidel, Felipe Arretche

Published Nov 27, 2018• 5 citations
Publisher

Abstract

Electron scattering by rare-gas dimers is studied for very low incident energies using the zero range potential (ZRP) method. Beyond the traditional ZRP, we consider an alternative formulation accounting for the atomic polarization, inspired in the modified effective range theory. The scattering calculations are reported in fixed nuclei, rigid rotor, and rovibrational approximations, the first two being analytical. An expression for the electron-molecule scattering length is obtained. We find that short-range interactions are the dominant mechanism for rotational transitions in electron scattering by rare-gas dimers, while the long-range interactions may be neglected. Our results show how the elastic, rotational, and rovibrational cross sections depend on the electron-atom scattering length, on the molecular parameters, and also on the inclusion of polarization effects. The principle of detailed balance is discussed in the context of the ZRP method. Finally, we show that the rovibrational coupling considerably affects the rotational cross sections when the rotational constant becomes comparable to the vibrational constant.

DOI
10.1103/physreva.98.052707

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physics.atom-phCross-listedarXiv:2603.04465•Mar 5, 2026
Electron scattering by rare-gas dimers is studied for very low incident energies using the zero range potential (ZRP) method. Beyond the traditional ZRP, we consider an alternative formulation accounting for the atomic polarization, inspired in the modified effective range theory. The scattering calculations are reported in fixed nuclei, rigid rotor, and rovibrational approximations, the first two being analytical. An expression for the electron-molecule scattering length is obtained. We find that short-range interactions are the dominant mechanism for rotational transitions in electron scattering by rare-gas dimers, while the long-range interactions may be neglected. Our results show how the elastic, rotational, and rovibrational cross sections depend on the electron-atom scattering length, on the molecular parameters, and also on the inclusion of polarization effects. The principle of detailed balance is discussed in the context of the ZRP method. Finally, we show that the rovibrational coupling considerably affects the rotational cross sections when the rotational constant becomes comparable to the vibrational constant.
Semiclassical calculations of the quasi-elastic l-mixing and inelastic n,l-changing processes in thermal collisions of a Rydberg sodium atom with rare-gas atoms (Ne, Ar, Kr and Xe) as well as and atoms with Ne are presented in a wide range of principal quantum numbers. The main emphasis is put on the study of the effects in the Rydberg-atom - rare-gas-atom collisions associated with both the short- and long-range (polarization) parts of the electron - perturber interaction. It is shown that the polarization interaction between the highly excited electron and the Ne atom provides the major contribution to the cross section of the l-mixing and n, l -changing transitions. We show that the Ramsauer - Townsend effect in slow electron scattering by the heavy rare-gas atoms significantly affects the values of the cross sections, particularly for the inelastic transitions with large energy transfer. A quantitative explanation of these phenomena is given using the recently developed semiclassical normalized perturbation theory for the Rydberg-atom - neutral collisions combined with the modified effective range theory for scattering of slow electrons by the rare-gas atoms.
The numerical approach to calculating the SSS-matrix poles associated with virtual states in electron-molecule collisions is proposed within the modified effective-range theory frame. The SSS-matrix continuation into the complex momentum plane is possible thanks to the analytical properties of modified Mathieu functions, that is, the exact solutions of the Schr\"odinger equation with the long-range polarization potential ($\ensuremath{\sim}{r}^{\ensuremath{-}4}$). The short-range electron-molecule interaction is included in the introduced numerical approach by model comparison with experimental integral, differential, and momentum-transfer elastic cross sections. The influence of the polarization potential on the virtual-state pole positions is analyzed for nonpolar targets such as N2,CH4,CO2{\mathrm{N}}_{2}, {\mathrm{CH}}_{4}, {\mathrm{CO}}_{2}N2​,CH4​,CO2​, and SF6{\mathrm{SF}}_{6}SF6​. The relation between the SSS-matrix pole position and the sss-wave scattering length is discussed.
This article presents the Zero Range Potential (ZRP) approximation as an alternative to treat quantum scattering problems. The main focus is to provide an undergraduate-level derivation of the ZRP boundary condition that describes the interaction between an electron and a potential, using the spherical-potential-well analytical solutions. The validity of the approximation is discussed qualitatively and quantitatively. Finally, the ZRP approximation is applied to the scattering of an electron by an atom, comparing the results obtained with modern experimental measurements.
The scattering lengths and effective ranges for collisions of ground state Be atoms interacting via the X 1Σ + g molecular state of the Be 2 dimer are calculated for two published X 1Σ + g potentials. A new ab initio X 1Σ + g potential is presented with its vibrational energies and rotational constants. The scattering parameters calculated with it and with the existing potentials are compared. Simple formulae showing how the scattering parameters are influenced by adiabatic coupling to electronic motion are derived within the semi-classical formulation and evaluated for the potentials considered. The formulae imply that a semi-classical account of adiabatic coupling can be made by increasing each atomic mass by one electron mass. © 2007 IOP Publishing Ltd.
In a recent paper, Reisfeld and Asaf [Phys. Rev. A 49, 348 (1994)] suggested a simple model explaining an observed correlation between the electron scattering lengths and electric polarizabilities of rare-gas atoms. They proposed an electron-target interaction potential consisting of a short-range hard-core repulsive part plus a long-range dipole polarization potential, and used the Born approximation to evaluate the scattering length. We show that for this model the scattering length may be evaluated analytically and that theoretical predictions based on an exact expression disagree with experimental data.
Full-dimensional quantum scattering calculations are reported for ro-vibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H2_22​-H2_22​ system. Several near-resonant ro-vibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low energy resonant features in the energy dependence of the cross sections are identified. The computed results are in agreement with total cross sections reported in previous experimental results, including resonant features in the energy dependence of the cross section. In particular, low-energy cross sections show a strong resonant feature associated with an l=3l=3l=3 partial wave in the incident channel. Rate coefficients for several inelastic rotational and ro-vibrational transitions are reported for temperatures ranging from 0.10.10.1 K to 200200200 K and they display a maximum between 111 K-101010 K reflecting the important contributions from the l=3l=3l=3 shape resonance that occurs around 2.5 K.