Isomeric effects on the electron impact scattering for selected five membered heterocyclic ring molecules

Abstract

We present electron scattering cross-sectional data for selected isomers of the five-membered ring molecules, specifically oxazole and isoxazole, thiazole and isothiazole, and imidazole and pyrazole. The ab-initio R-matrix method, incorporating static exchange polarization approximations, is employed for this calculation from energy range 0.1 eV to 20 eV. Three shape resonances are identified and characterized in each system, consisting of two π* and one σ* shape resonances. Notably, thiazole and isothiazole exhibit additional σ* resonance which is which is at a lower energy than other σ* resonance. The calculated resonance positions align well with available experimental as well as theoretical data. We also performed electronic structure calculations to aid in characterization of resonances. Comparison of the scattering cross-sectional data with their respective isomers reveal marginal differences in the magnitude of the elastic cross section particularly below 1 eV. This discrepancy may be attributed to variations in the long-range electronic dipole contribution to the electron-molecule interaction process. Further, to understand dependency of dipole moment on elastic cross section, we performed a fitting procedure for the elastic cross sections at 0.1 eV with square of the dipole moment of all the five membered ring molecules studied here. The fitting formula so obtained was used to estimate the cross section for other three five membered ring molecules: Furan, Thiophene and Pyrrole. Additionally, total ionization cross sections are computed using the binary-encounter-Bethe (BEB) model, demonstrating nearly identical results when compared with their isomers. Our findings offer insights into the influence of structural changes on the electron scattering data, providing guidance for other theoretical investigations.