Elastic and vibrationally inelastic scattering of low-energy electrons from propane

In a crossed-beam experiment, differential cross sections (DCS) for elastic and vibrationally inelastic scattering of electrons from propane have been measured in the energy range E = 0.5–10 eV. Absolute values are obtained by using e−–He scattering as a reference system. For elastic scattering, the measured DCS are analysed by phase-shift analysis and modified effective-range theory and then extrapolated into the experimentally inaccessible regions. In this way, the complete set of elastic DCS for E = 0–10 eV and θ = 0°–180° is obtained. Integral and momentum transfer cross sections are determined, which are compared with the results of electron transmission and swarm experiments. For vibrationally inelastic scattering, the observed vibrational excitation (VE) processes are divided into three groups: (i) CHx stretching modes, with a mean energy loss of ΔE = 366 meV; (ii) CHx deformation modes, with ΔE = 175 meV; (iii) CC carbon chain vibrations, with ΔE = 122 meV. Absolute differential and integral cross sections are determined for each of the three mode groups. Two principal VE mechanisms are responsible for the observed processes: direct VE for energies below 3 eV and resonant VE for energies around 7–8 eV. The Born dipole approximation is used to analyse the data in the region of direct VE at low energies.