A. R. Lopes

Electron collisions with isomers of C4H8 and C4H10

We report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by several isomers of the C4H8 molecules, such as isobutene, trans-2-butene, cis-2-butene, skew-1-butene and syn-1-butene, and by two isomers of C4H10, the isobutane and the butane molecules. To calculate the cross sections, we use the Schwinger multichannel method with pseudopotentials (Bettega et al 1993 Phys. Rev. A 47 1111) applied at the static exchange level of approximation for incident energies from 10 to 50 eV. Although the C4H8 isomers have different geometric structures, our results show that the integral cross sections for each of these isomers present a broad shape resonance around 10 eV; our results also show that for all C4H8 molecular targets, integral cross sections are very similar in shape and magnitude. Similarities are also found in the momentum transfer and in the differential cross sections of these isomers. The same pattern is found in the cross sections of the C4H10 isomers. Through comparison of the integral and momentum transfer cross sections of 1,3-butadiene (C4H6), trans-2-butene (C4H8) and butane (C4H10), all belonging to the C2h group and having similar structures, we discuss the role of the hydrogen atoms in the scattering process by these molecules. Further we show that the integral elastic cross sections of all simple hydrocarbons present strong similarities after a scaling. We present a simple geometric model for this scaling that works quite well for a whole family of CnHm molecules (with combinations of n = 1, 2, 3, 4 and m = 2, 4, 6, 8, 10).

Elastic scattering of low-energy electrons by C 3 H 4 isomers

We report integral, differential, and momentum-transfer cross sections for elastic scattering of low-energy electrons by the C{sub 3}H{sub 4} isomers allene, propyne, and cyclopropene, which belong to the D{sub 2d}, C{sub 3v}, and C{sub 2v} groups, respectively. We use the Schwinger multichannel method with pseudopotentials [Bettega et al., Phys. Rev. A 47, 1111 (1993)] at the static-exchange approximation to compute the cross sections for energies up to 40 eV. We compare our results with available experimental results and find very good agreement. Our results confirm the existence of the shape resonances in the cross sections of allene and propyne, and the isomer effect, both reported by the experimental studies.

Halogenation effects on electron collisions with CF3Cl, CF2Cl2, and CFCl3

We report differential and integral elastic cross sections for low-energy electron collisions with CF3Cl, CF2Cl2, and CFCl3 molecules for energies ranging from 0.1 eV to 30 eV. The calculations were performed using the Schwinger multichannel method with pseudopotentials in the static-exchange and static-exchange plus polarization approximations. The influence of the permanent electric dipole moment on the cross sections was included using the Born closure scheme. A very good agreement between our calculations and the experimental results of Jones [J. Chem. Phys. 84, 813 (1986)], Mann and Linder [J. Phys. B 25, 1621 (1992); 25, 1633 (1992)] and Hoshino et al. [J. Chem. Phys. 138, 214305 (2013)] was found. We also compare our results with the calculations of Beyer et al. [Chem. Phys. 255, 1 (2000)] using the R-matrix method, where we find good agreement with respect to the location of the resonances, and with the calculations of Hoshino et al. using the independent atom method with screening corrected additivity rule, where we find qualitative agreement at energies above 20 eV. Additional electronic structure calculations were carried out in order to help in the interpretation of the scattering results. The stabilization the lowest σ(∗) resonance due to the exchange of fluorine by chlorine atoms (halogenation effect) follows a simple linear relation with the energy of the lowest unoccupied molecular orbitals and can be considered as a signature of the halogenation effect.

Electron collisions with nitromethane

We present elastic cross sections for low energy electron-collisions with the nitromethane molecule. We compare our results for the π* and the σ* shape resonances position with the available experimental data.