Experimental and theoretical study of low energy differential elastic electron scattering from acrylonitrile (C2H3CN)

We report new experimental and theoretical differential elastic scattering cross sections (DCSs) for low-energy electron scattering from acrylonitrile (C2H3CN), together with integral and momentum-transfer cross sections derived from the measured DCSs. The experimental measurements were performed using the relative flow method with helium as the standard gas in a crossed electron-molecular beam arrangement. The measurements cover incident electron energies from 0.7 to 30 eV and scattering angles between 10° and 130°. The experimental DCSs are compared with Schwinger multichannel calculations employing pseudopotentials within the static-exchange plus polarization (SEP) approximation for electron-impact energies up to 30 eV. Owing to the large permanent dipole moment of acrylonitrile, the Born-closure procedure was applied to account for the long-range dipole interaction. The large dipole moment also suggests the possible existence of a dipole-bound state, in which the excess electron occupies a highly diffuse orbital localized in the positive region of the molecular electrostatic dipole potential. To place the acrylonitrile results in the context of the nitrile series, we compare them with previously published experimental data for hydrogen cyanide (formonitrile, HCN) [S. K. Srivastava, H. Tanaka, and A. Chutjian, J. Chem. Phys. 69, 1493 (1978)] and acetonitrile (CH3CN) [M. Zawadzki and M. A. Khakoo, J. Chem. Phys. 149, 124304 (2018)]. The comparison indicates that, while the strong forward scattering is primarily governed by the permanent dipole moment, acrylonitrile exhibits enhanced scattering at larger scattering angles (θ > 80°), which may be associated with low-lying π* resonances facilitated by its extended π-conjugated structure.