Electron collisions with phenol: Total, integral, differential, and momentum transfer cross sections and the role of multichannel coupling effects on the elastic channel

Abstract

We report theoretical and experimental total cross sections for electron scattering by phenol (C6H5OH). The experimental data were obtained with an apparatus based in Madrid and the calculated cross sections with two different methodologies, the independent atom method with screening corrected additivity rule (IAM-SCAR), and the Schwinger multichannel method with pseudopotentials (SMCPP). The SMCPP method in the Nopen-channel coupling scheme, at the static-exchange-plus-polarization approximation, is employed to calculate the scattering amplitudes at impact energies ranging from 5.0 eV to 50 eV. We discuss the multichannel coupling effects in the calculated cross sections, in particular how the number of excited states included in the open-channel space impacts upon the convergence of the elastic cross sections at higher collision energies. The IAM-SCAR approach was also used to obtain the elastic differential cross sections (DCSs) and for correcting the experimental total cross sections for the so-called forward angle scattering effect. We found a very good agreement between our SMCPP theoretical differential, integral, and momentum transfer cross sections and experimental data for benzene (a molecule differing from phenol by replacing a hydrogen atom in benzene with a hydroxyl group). Although some discrepancies were found for lower energies, the agreement between the SMCPP data and the DCSs obtained with the IAM-SCAR method improves, as expected, as the impact energy increases. We also have a good agreement among the present SMCPP calculated total cross section (which includes elastic, 32 inelastic electronic excitation processes and ionization contributions, the latter estimated with the binary-encounter-Bethe model), the IAM-SCAR total cross section, and the experimental data when the latter is corrected for the forward angle scattering effect [Fuss et al., Phys. Rev. A 88, 042702 (2013)].

Integral cross sections for electron impact excitation of vibrational and electronic states in phenol

“…In addition, Neves et al 21 found some evidence for a higher-lying shape resonance enhancing the phenol cross sections vis à vis those of benzene. Support for the existence of that resonance was also found in our Schwinger Multichannel Method with Pseudo-potentials (SMCPP) calculations for the elastic channel 20 and our experimental total cross section measurements. 20 As the decay of a resonance into a given scattering channel or channels is often most easily seen through the measurements of excitation functions or integral cross sections, 31 we were thus also interested to see if the proposed resonance manifested itself in our vibrational-mode and electronic-state ICSs.…”

“…1 for the CH-stretch and CH-stretch overtone (2 × CHstretch) being consistent with that observation. We had previously observed that there is some evidence, in our elastic cross section calculations 3,20 and total cross section measurements, 20 for the existence of a broad shape resonance for incident electron energies in the ∼10-20 eV range. Further support for this notion can be found in Fig.…”

“…23 not this apparent failure is due to the quite detailed mixture of singlet and triplet states within bands 3 and 4, and some form of interchannel coupling going on between them, 20 or another reason, awaits a detailed ab initio theoretical analysis. Finally, in regards to band 5, we simply note that the energy dependence of its ICSs is very similar to that previously seen (see Fig.…”

“…When those factors are combined in quadrature, the errors on our ICS (see Tables I and II) are found to be in the range 7%-83%, the precise error depending on the inelastic channel in question with the highest uncertainties being found for band 1 (unresolved triplet) electronic-states and the CH-stretch overtone. We have also previously described our IAM-SCAR computations many times, 20,30,[33][34][35] so that only a précis need be given here. Basically, an atomic optical potential scattering model calculates all the phase shifts for each of the atoms that comprise the molecule in question (i.e., carbon, oxygen, and hydrogen for phenol).…”

“…To this end, we have conducted a series of joint experimental and theoretical studies looking at the behaviour of electron-phenol scattering processes. Specifically, results for phenol's (e, 2e) triple differential cross sections (DCSs), 19 elastic scattering and total cross sections (TCS), 20 vibrational excitation differential cross sections, 21 and excited electronic-state differential cross sections 22 have all thus far been reported. In addition, a) Author to whom correspondence should be addressed.…”