Positronium formation in methanol and ethanol

Cross sections for the formation of positronium (Ps) in collisions of positrons with methanol and ethanol molecules, QPs, have been measured for positrons of incident energies from 3 to 40 eV. The threshold energies for Ps formation were found to be 4.0 ± 0.2 eV and 3.5 ± 0.5 eV, respectively. QPs for the two molecules are very similar in size and energy dependence, suggesting that Ps formation is associated preferentially with the OH group, whereas (Qtot–QPs), where Qtot is the total scattering cross section, is related more to the physical size of the molecules.