e^--Ar scattering length from drift velocities measured in argon-hydrogen mixtures

Abstract

We present experimental data for drift velocities of very low energy electrons in a 5.45% hydrogen-argon mixture and the analysis of these data to determine the e--Ar scattering length. The addition of a small fraction of hydrogen to argon enables experiments to be made with very low-energy electron swarms without the use of very high gas densities, thus reducing the uncertainty in the e--Ar cross section derived from the experimental data. A scattering length of -1.459 a0 is found, lying between the previous swarm determination and that obtained from time-of-flight (TOF) beam measurements. Pressure effects on the transport coefficients measured in earlier experiments are discussed, and evidence presented for a large departure from the Einstein relation at gas densities of 3*1020 cm-3.

High-resolution total-cross-section measurements for electron scattering from Ar, Kr, and Xe employing a threshold-photoelectron source

“…The values were −1.365, −3.06, and −5.13 a 0 for Ar, Kr, and Xe, respectively. It was found that the scattering lengths for these rare-gas atoms obtained in the previous studies [7][8][9][10]16,18,19,21,23,59,61] show larger absolute values compared to the present values due to the overestimation of the cross sections at very low energies below 100 meV, where direct measurements in the single-collision condition have not been reported.…”

“…However, measurements of the total cross section for electron scattering from Ar, Kr, and Xe using this technique have not been reported. Electron-swarm techniques have also been used to derive cross-section data, such as momentum-transfer cross sections, for rare-gas atoms at very low energy [15][16][17][18][19][20][21][22][23]. The method provided the information over an energy range from about 10 meV to a few eV, which has been very difficult to access by the standard single-collision experiments.…”

Theory and simulation of spectral line broadening by exoplanetary atmospheric haze

“…has been measured from low-energy drift velocities of electrons in an H-Ar mixture, to be L Ar = −1.46 a 0 , (Petrovic et al 1995), where a 0 is the Bohr radius. Admittedly, the haze constituency will more likely be in the form of carbonbearing, water, and other complex molecules, but for purposes of computational efficiency, interacting sodium atoms with rare-gas atomic samples offers a convenient way to calculate many-body mean-field aspect of this theory.…”

Kinetic phenomena in charged particle transport in gases, swarm parameters and cross section data

“…or perhaps even a pipedream). New challenges for swarm physics lie in developing experiments with radio frequency fields to match the recent theoretical and numerical predictions (Petrović et al 1995) and to venture to higher mean energies to cover the energy region that is of interest for plasma modelling. Surprisingly, very high energies have been covered better than the range of moderate energies by low pressure high E/N experiments .…”