Elastic scattering of electrons by methane molecules

Abstract

Vibrational elastic, rotationally summed cross sections for electron collisions with CH4 are calculated with ab initio static-exchange interactions and using a symmetry-adapted, single-center-expansion representation for the close-coupling equations. The correlation forces are included through densityfunctional theory and via a near-Hartree-Fock self-consistent-field description of the target wave function. Integral and diff'erential cross sections are calculated over a broad range of collision energies, from the shape resonance region up to 50 eV. Comparisons with experiments and with previous calculations show that the present results indeed exhibit very good overall accord with measurements at these collision energies and describe very efhciently the electron angular distributions as given by a very broad range of measurements.

Ramsauer-Townsend minimum in methane — modified effective range analysis

“…The high value of dipole polarizability makes it difficult to determine theoretically the low energy elastic collisions parameters. Different asymptotic models of the polarization potential influence significantly the depth and the position of the R-T minimum, so alternative forms of polarization are frequently used in separate energy regions [16,17,24,25]. Therefore, no consensus has been obtained on CH 4 cross sections in the R-T minimum range so far, as it has also been documented by numerous alternative sets of data used for modelling electron diffusion processes and gas discharges in methane and its mixtures [27,29].…”

“…Measurements by Zecca et al [47], coinciding within the error bar with those of Jones, are given only at a few energy points and with only two-digit precision, so they do not introduce any new information and they are not shown in Figure 3. (2) Experimental integral elastic cross sections in our range of interest were given (using the closed-coupled model of Gianturco et al [25]) in Bundschu et al [26] at 0.6-2 eV and by Sohn et al [18] at 0.2-2 eV (using a partial-wave fit). We note that the measurements of Sohn et al [18] above and below 0.5 eV come from two distinct experimental series, so some differences in normalization and/or analysis procedures are not to be excluded.…”

“…For the theoretical approach, methane is one of the most intensively studied molecules [16][17][18][19][20][21][22][23][24][25][26][27][28]. The high value of dipole polarizability makes it difficult to determine theoretically the low energy elastic collisions parameters.…”

Optical potentialmethod for electron scattering by molecule

“…Це дозволяє ро-зглядати молекулу, як центрально-симетри-чну систему. Такими методами є набли-ження сферичних [7] та одноцентровиx [8] потенціалів.…”

“…Наприклад, значення параметрів для аналітичного опису електронних густин для атома P, розрахованих у локальному на-ближенні ТФГ,наведено у [11]. Слід відмі-тити, що у більш послідовних підходах [7] та [8] -імпульс Фермі для n-го атома молекули, виражений через повну електронну густину…”