Absolute electron impact ionization cross-sections and polarizability volumes for the C2 to C6 methanoates and C3 to C7 ethanoates

Absolute total positive ion electron impact ionization cross-sections from 15 to 285 eV are reported for the C-2 to C-6 methanoates (formates) and the C-3 to C-7 ethanoates (acetates), including all isomers. The reproducibility of the measured cross-sections over the full energy range is better than +/- 4%, and absolute cross-sections measured for a series of reference species (N-2 and inert gases) are in excellent agreement with values reported by several other groups claiming accuracies of around 5%. A monotonic relationship is shown to exist between the maximum ionization cross-sections for the esters, reported here, the C-1 to C-4 alcohols, reported previously, and the total number of carbon atoms in the skeletal chain. The relationship provides a useful means for estimating unknown cross-sections. Polarizability volumes for esters may be estimated using a previously established correlation with the maximum ionization cross-section, and for the four species for which published data are available the predictions are in good agreement with experiment. Finally, the experimental data are compared with calculations carried out using the binary encounter Bethe (BEB) method for the calculation of total ionization cross-sections. (c) 2005 Elsevier B.V. All rights reserved.