Elastic and electronically inelastic scattering of electrons by 2H-pyran and 4H-pyran molecules

Abstract

We report on elastic and electronically inelastic integral and differential cross sections for electron collisions with the 2H-pyran and 4H-pyran molecules. The scattering calculations were performed with the Schwinger multichannel method and aimed to (i) investigate the formation of resonant states, (ii) assign and compare the resonance spectrum of these isomers, and (iii) evaluate the influence of multichannel coupling effects upon elastic and electronically inelastic scattering processes. In the elastic channel, calculations carried out at the static-exchange and static-exchange plus polarization levels of approximation revealed the presence of three shape resonances for each one of the pyran isomers. For the 2H-pyran molecule, we found two resonances related to the formation of long-lived π∗ anion states that are centered at 1.38 or 1.32 eV (π1∗) and 4.54 or 4.46 eV (π2∗), depending on the polarization model used in the calculations, and a broad resonance of σ∗ character located around 9.50–10.00 eV. The resonances observed in the case of the 4H-pyran molecule have the same character with centers located at 2.08 or 2.20 eV (π1∗), 3.92 or 3.94 eV (π2∗), and 9.24–10.00 or 9.50–10.00 eV (σ∗), depending on the polarization model used in the calculations. The difference in the position of the resonances when comparing the results for the 2HPY and 4HPY molecules is explained in terms of the inductive effect. The electronically inelastic calculations employed the minimal orbital basis for single configuration interactions strategy and considered up to 129 open channels for 2H-pyran and up to 249 open channels for 4H-pyran. According to these levels of channel coupling, we computed integral and differential cross sections for the excitation from the ground state to the 13A′, 23A′, 11A′′, and 21A′ electronic excited states of 2H-pyran and to the 13B2, 13A1, 11B1, and 11B2 electronic excited states of 4H-pyran. As a general trend, for both isomers, we observed that the magnitude of the cross sections is reduced as more channels are considered open in the scattering calculations. We also obtained the total ionization cross sections for 2H- and 4H-pyran using the binary-encounter-Bethe model, which next was summed to the elastic and electronically inelastic cross sections to estimate the total cross sections. As a whole, these results correspond to the first set of cross sections for these targets published to date. Such an effort is aimed at addressing the demand of different communities regarding the expansion of the cross section data set for electron collisions with molecules of technological, environmental, and biological relevance, a need that has been raised by several reviews on the subject.