Joint experimental and theoretical study on low-energy elastic electron scattering by gaseous alkynes: Differential cross sections, shape resonances, and methylation effects

A detailed comparison of experimental and theoretical elastic cross sections for low-energy electron scattering by ethyne (C2H2), taken earlier in our group by Gauf et al. [Phys. Rev. A 87, 012710 (2013)], and some of its methylated derivatives, propyne (C3H4), and the isomers 1-butyne and 2-butyne (n-C4H6, n = 1, 2), taken here, are presented. The present differential cross sections were measured at incident electron energies ranging from 1 eV to 30 eV and for scattering angles from 5??? to 130??? using the relative flow method with an aperture gas source. Our earlier work was taken over a larger energy range of up to 100 eV. The theoretical calculations were carried out for impact energies up to 30 eV, employing the Schwinger multichannel method with pseudopotentials in the static-exchange plus polarization approximation. In addition to the differential cross sections, we present the integral and momentum transfer cross sections with which we discuss the shape resonances present in these systems and other physical phenomena, such as the presence of Ramsauer-Townsend minimum. We also compare our theoretical and experimental results with previous data that are available in the literature.