Shape and Core-Excited Resonances in Thiophene

Abstract

We present a comprehensive study of resonance formation in electron collisions with thiophene. Detailed calculations have been performed using the ab initio R-matrix method. Absolute differential cross sections for electron impact excitation up to 18 eV and for two scattering angles, 90 and 135°, have been measured. Agreement between the calculated and measured experimental cross sections is very good. Three shape resonances previously described, two of π* character and one σ*, as well as a number of resonances of core-excited or mixed character are identified and characterized in the calculations. The measured cross sections provide experimental confirmation for a number of the core-excited resonances. The link between these resonances and prior DEA experiments is discussed.

UKRmol+: A suite for modelling electronic processes in molecules interacting with electrons, positrons and photons using the R-matrix method

“…We note that the experimental cross sections were not normalized to calculated values. The figure also shows that two core-excited resonances (of symmetry 2 B 1 and 2 A 2 ) are visible in both cross sections: the shift to higher energies of the calculated resonances is a well known effect due to an incomplete description of the polarization effects [72].…”

“…Elastic integral and differential (using an external program) cross sections can be calculated very accurately, although polar molecules present more of a problem [69,70]. The suite is able to model electronic excitation for small and mid-size molecules very accurately as well as describe their coreexcited resonances [71,72]. Among the largest targets studied (in terms of number of atoms in the system) are the molecular clusters pyridine-(H 2 O) 5 and thymine-(H 2 O) 5 for which SE and SEP calculations have been performed [42,43].…”

“…Cross sections for excitation into the second triplet state of thiophene for an electron scattering angle of 90 • . The EEL spectrum was measured for an energy loss of 4.61 eV[72] and. Two core-excited resonances are clearly visible as peaks below 10 eV in both results.…”

Electron collisions with molecules and molecular clusters

“…Two examples of the predictive power of R-matrix calculations are given by the core-excited resonances in pyrimidine [32] and thiophene [33]. For these targets EEL spectra have confirmed, by measuring excitation functions and cross sections for electronic excitation to bands (for the former target) or specific states (for the latter), the presence of many of the resonances determined theoretically.…”

“…together with those measured for 90 • and 135 • . Details of the calculation and experiment can be found elsewhere [33].…”