Low-energy positron scattering from iodomethane

We report experimental total cross sections (TCSs) and calculated elastic integral cross sections (ICSs) for positron collisions with iodomethane (methyl iodide, CH3I). The experimental TCSs were obtained with a linear transmission technique, for energies from 0.1 up to 50 eV. The present TCS data agree well with those previously reported (Kimura et al 2001 J. Chem. Phys. 115 7442) at higher energies (above 7 eV), but significant discrepancies are found at the lower energies. The present ICS computations were performed with the Schwinger multichannel method (SMC) and the Born dipole approximation in the incident energy range from 0.1 eV up to 10 eV. Iodomethane poses a great challenge to theoretical descriptions of the collisions dynamics. In addition to the neglect of inelastic channels, the main difficulty found in the SMC approach is related to numerical limitations that prevent a thorough description of correlation–polarization effects. Although our ICS calculations do not compare well with the present TCS data, the results are encouraging, as iodomethane would challenge all the presently available computational approaches. (paper)