Effective configurations in electron-molecule scattering. II

We present results of the application of the Schwinger multichannel method using effective configurations [Azevedo et al.. Phys. Rev. A 61, 042701 (2000)] to study special features of low-energy electron-molecule scattering, such as (i) the shape resonance in e(-)-N-2 scattering: (ii) the Ramsauer-Townsend minimum in e(-)-CH4 scattering: and (iii) a Feshbach resonance in e(-)-H-2 scattering (in a two-channel coupling calculation including polarization effects). In all cases, we find that the use of effective configurations to describe polarization effects allows a substantial reduction of the configuration spacer without any loss of quality of the results. The present applications (together with our previous study of nonresonant electron-H-2 scattering) indicate that this technique will be very useful in the analysis of more complex systems.63

Electron-impact electronic excitation of molecular nitrogen using the Schwinger multichannel variational method

The Schwinger multichannel method is applied to study the low-energy electron-impact excitation of molecular nitrogen. The scattering amplitudes are obtained within the minimal orbital basis for single configuration interactions (MOBSCI) level of approximation, for impact energies from near threshold up to 30 eV. Through the use of the MOBSCI strategy we have performed a close-coupling calculation for up to nine states, including the ground state and all singlet and triplet states resulting from the pi(u)->pi(g) transitions. Integral and differential cross sections for the X (1)Sigma(+)(g)-> A (3)Sigma(+)(u), W (3)Delta(u), B-' (3)Sigma(-)(u), a(') (1)Sigma(-)(u), and w (1)Delta(u) electronic transitions are presented and compared with available experimental data and also with other theoretical results.75

Chemical characterization of passion fruit (Passiflora edulis f. flavicarpa) seeds

The aim of this study was to determine the chemical characteristics of passion fruit seeds and their oil for possible use in human food and reduction of organic waste from fruit industrialization. Passion fruit seeds were analyzed for moisture, lipids, proteins, ash, fibers, titratable acidity, pH, soluble solids and antioxidant activity. The oil was characterized for parameters such as acid value, saponification, iodine and peroxide. The content of oil extracted demonstrates that it has good potential for  industrial utilization. According to analyses, the oil has characteristics similar to conventional edible oils such as soybean, and may be a new source of human consumption. Passion fruit seeds have high nutritional value, proving to be a promising product, mainly because it contains  significant amounts of proteinase. Therefore, passion fruit seeds and their oil should be used as raw material in the food, chemical and pharmaceutical industry, as they have beneficial features.Key words: Industrial utilization, characterization, by-products

SPIN EXCHANGE IN ELASTIC-E-O2 COLLISIONS

Recent experiments using polarized electron beams have shown that spin-exchange effects for elastic collisions with O2 and NO are much smaller than for Na atoms. We report calculated spin-flip differential cross sections for elastic collisions of polarized electrons with O2 in agreement with experiment. In general, we can attribute large variations of the spin-flip differential cross sections to resonances and interference effects. Such features arising from interference, however, may be washed out in the molecular case due to the average over orientations. Calculations with oriented O2 show strong exchange effects as for Na.68111698170

Cross sections for collisions of low-energy electrons with the hydrides PH3, AsH3, SbH3, SnH4, TeH2, and HI

We calculated integral and differential cross sections for scattering of low-energy electrons by two groups of hydrides from 10 to 30 eV. The first group is composed by the hydrides of elements in the same column of the Periodic Table and includes PH3, AsH3, and SbH3. The second group is formed by hydrides in the same row and includes SnH4, SbH3, TeH2, and HI. The calculations employed the Schwinger multichannel method with norm-conserving pseudopotentials [M.H.F. Bettega, L.G. Ferreira, and M.A.P. Lima, Phys. Rev. A 47, 1111 (1993)]. Our goal is to find similarities and differences in the cross sections in these two groups. (C) 1996 American Institute of Physics.10531029103

Electronic excitation of XH4 (X = C,Si,Ge,Sn,Pb) by electron impact

We calculate integral cross sections for the electronic excitation to the T-3(2) states of XH4 (X= C,Si,Ge,Sn,Pb) by electron impact. This is the lowest-lying excited state of these molecules. Our results were obtained with the Schwinger multichannel method with pseudopotentials at the two-state level of approximation. In the case of CH4 we compare our results with previous results of an all-electron calculation obtained at the same level of approximation, in which case we found an excellent agreement between the two calculations. Though these molecules are very similar, after discarding the cores, as the pseudopotential technique does, the inelastic cross sections are very distinctive and do not have a monotonic behavior with increasing proton number Z of the central atom.5764987499

Feshbach projection operator approach to positron annihilation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We present a theory of vibrationally enhanced positron annihilation on molecules based on the Feshbach projection operator formalism. A key aspect of the present approach is the fact that no direct vibrational excitation is assumed, i.e., the attachment mechanism is electronic in nature, arising from positron-electron correlation-polarization forces, and energy transfer to the nuclei essentially follows from the difference between the potential-energy surfaces of the isolated target and the positron-molecule compound; moreover, no a priori assumption is made on the character of the transient (bound or virtual state). An approximate relation between the annihilation parameter Z(eff) and the vibrationally summed cross section is presented, as well as a hierarchy of approximations that may allow for elaborate model calculations. We also discuss how important aspects of the annihilation process are taken into account in the present theory, such as isotope effects, vibrational energy redistribution and relative strengths among vibrational resonances. For completeness, semiempirical model calculations for acetylene and ethylene are presented. Despite the stringent approximations employed in this simplest version of the theory, fair agreement with experimental data was obtained in the vicinity of 0 -> 1 thresholds.805Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

25-state calculation for e(-)-Na-2 scattering

We use the Schwinger multichannel method with pseudopotentials to study low energy e(-)-Na-2 scattering. Our cross sections, for impact energies from 0 to 10 eV, include polarization effects and up to 25 open channels related to all electronic states lying below 3.5 eV. Our results predict prominent threshold effects due to a very intense coupling between the B(1)Pi(u) state and the elastic channel in an energy region where there is no experimental data. Our total 25-state cross sections are in very good agreement with available experimental data for energies below about 4 eV. [S0031-9007(98)07561-9].81183832383

Annihilation dynamics of positrons in molecular environments: Theoretical study of low-energy positron-C2H4 scattering

We present a theoretical study of low-energy positron-C2H4 scattering using the Schwinger multichannel method. We calculated integral cross sections and the annihilation parameter Z(eff) for positron impact energies from 0.001 to 6 eV. We have used up to 23 112 configurations in a fully a initio calculation. Our results are in excellent agreement with available experimental data. As seen experimentally, at low energies, our calculated Z(eff) and cross sections are very large. We attribute this behavior to virtual positronium formation.7761028103

Effective configurations in electron-molecule scattering

We present a more efficient way of treating polarization effects in the scattering of low-energy electrons by molecules within the Schwinger multichannel (SMC) method. We propose to expand the scattering wave function in a set of functions of N + 1 electrons that describe the scattering in an effective way, which allows the use of a small number of functions to describe the polarization effects. As a first test, we apply the method to the scattering of electrons by the H-2 molecule. We calculate elastic integral and differential cross sections, and we obtain excellent results with a reduction in the number of configurations of up to 98% when compared to the traditional method used in the SMC method. This is a substantial size reduction of all matrices involved in the SMC method and, as a consequence, it represents a promising technique for treating more complex molecular systems.61