Elastic scattering and rotational excitation of a polyatomic molecule by electron impact: Acetylene

We have calculated differential, integral, momentum transfer, and partial cross sections for elastic scattering and rotational excitation of C ₂H₂ by 10 eV electrons. The effective potential includes static, exchange, and polarization interactions calculated by the INDOX/1s method and the semiclassical exchange approximation with adiabatic polarization at large electron-molecule distances. The scattering is treated by well converged rotational close coupling using the centrifugal dominant scheme to select the channels included and including up to 32 coupled channels for a given total angular momentum. The calculated integral cross sections for pure elastic scattering and rotational excitation are 54.5 and 41.4a₀ ², respectively. These are much larger than the values (34.4 and 18.6a₀²) previously [K. Onda and D. G. Truhlar, J. Chem. Phys. 71, 5107 (1979)] calculated for the isoelectronic molecule N₂ at this energy. This illustrates how the greater spatial extent of C ₂H₂ greatly increases the cross sections for pure elastic and rotationally inelastic scattering.