Application of the method of continued fractions to multichannel studies on electronic excitation ofH2by electron impact

Abstract

In the present work, the method of continued fractions at a five-channel close-coupling level of approximation is applied to study the low-energy electron-impact excitation in linear molecules. Particularly, cross sections for the X 1 ⌺ g ϩ →b 3 ⌺ u ϩ , X 1 ⌺ g ϩ →a 3 ⌺ g ϩ , and X 1 ⌺ g ϩ →c 3 ⌸ u transitions in H 2 in the ͑15-40͒-eV energy range are reported. As in our early two-state studies, no orthogonality constraint between the bound and continuum orbitals is imposed and the one-electron exchange terms are considered explicitly. In general, our calculated cross sections are in good agreement with the results obtained by the four-state Kohn variational method. Comparison between our calculated results with available experimental data is encouraging.

Cross sections for electron-impact excitation of the H2molecule using the MOB-SCI strategy

“…For the incident energy of 30 eV, our DCS is better compared to the experimental data from Khakoo and Trajmar [13] and lies systematically below the theoretical results from Lima et al [22] (SMC). The DCS also lies below the results obtained by Lee et al [26] and Machado et al [28] (MCF), except for angles above 150 • , where our result is a little bit more backward peaked. Figure 1(d) shows the integral cross section (ICS) for the X 1 (+) g → b 3 (+) u electronic transition.…”

“…That is, the MOB-SCI result is smaller in magnitude if compared with the ICS obtained by the SMC two-state calculation [22] and compares very well with the measured values from Khakoo and Trajmar [14] and Wrkich et al [17]. The agreement with the theoretical results from [32,28] is fair, especially at higher energies. 3.3.6.…”

“…At 30 eV our result compares well with the experimental data only for larger angles. The good agreement between measured DCS and the results obtained in the four-state calculations from Parker et al [25] (complex-Kohn) and Machado et al [28] (MCF) points out that the coupling among b 3 (+) u , a 3 (+) g and c 3 (+) u triplet states, in the angular region from 15 • to around 90 • , would be very important. In figure 3(d) we see that, although strongly affected by the presence of resonant structures, our integral cross section is in very good agreement with available experimental data from [13,14] and [17].…”

“…The errors introduced in the extrapolation procedure used to derive the experimental cross section may explain the great discrepancy observed at this energy. With respect to the theoretical calculations from [32] (R-matrix) and [28] (MCF), our results reproduce the ICS energy dependence in shape, but not in magnitude. The differences are possibly related to the strategy used in the composition of the active space of coupled states.…”

Excitações eletrônicas por impacto de pósitrons via Método Schwinger multicanal

“…O mesmo não podemos dizer daárea de pósitrons. Entre os vários métodos teóricos usualmente utilizados para efetuar este tipo de estudo mencionamos: Schwinger multicanal[52,59], "Complex Kohn"[63], matriz R[64], onda distorcida[65] e frações continuadas[66].Porém, mesmo com substancial progresso naárea de elétrons,é difícil identificar trabalhos que discutam uma "fenomenologia" para o processo de excitação eletrônica. O atual "estado da arte" sugere que não existe uma visão intuitiva sobre excitação eletrônica deátomos e moléculas por colisão com léptons leves.Trabalhos desta natureza também chamam a atenção para o fato de que cada processo de espalhamento possui suas próprias peculiaridades.…”