Absolute electron impact ionization cross-sections for the C1 to C4alcohols

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.