Absolute electron impact ionization cross-sections for the C1 to C4 alcohols

Abstract

Absolute total positive-ion electron impact ionization cross-sections from a few eV above threshold to over 200 eV are reported for the C1 to C4 alcohols, including the isomers of propanol and butanol. Correlations between measured ionization cross-sections, ionization potential and molecular polarisability volume are explored and compared with data reported previously for perfluorocarbons, nitriles and mixed halocarbons. Small, but reproducible, differences between the isomers of the C3 and C4 alcohols have been used to estimate molecular volume polarisabilities for iso- and tertiary butanol. A C–OH functional group contribution to the total ionization cross-section has been deduced in line with bond contributions determined for a range of C–X (where X = C, H, F, Cl, Br, I, CN) bond types previously reported. The reproducibility of the measured cross-sections over the full energy range is better than ±2% and in some cases ±1%. Absolute cross-sections measured with the instrument are in excellent agreement with measurements for the inert gases and N2 made by several other groups claiming accuracies of around ±5%. Experimental data are compared with calculations using the Deutsch–Märk additivity method, the Binary Encounter Bethe method, and the polarisation model.