Formation of 2-propanol in condensed molecular films of acetaldehyde following electron impact ionisation-induced proton transfer*,**
Universität Bremen, Institute for Applied and
Physical Chemistry, Fachbereich 2
(Chemie/Biologie), Leobener Straße / NW 2, Postfach 330440,
Received in final form: 25 April 2016
Published online: 14 June 2016
Experimental studies on thin condensed layers of acetaldehyde have previously revealed that electron exposure at an energy above the ionisation threshold leads to formation of 2-propanol. However, the mechanism of this reaction remained unclear. Therefore, a computational approach is used to explore the electron-induced reactions of acetaldehyde yielding 2-propanol. Starting from hydrogen-bonded dimers of acetaldehyde we show that the initial ionisation event triggers proton transfer between the two acetaldehyde moieties resulting in a hydrogen-bonded complex of a [OCCH3] radical and a protonated acetaldehyde cation. Given an excess energy of up to 0.75 eV and a favourable arrangement, a methyl radical released upon dissociation of the CC bond within the [OCCH3] radical can migrate to the carbonyl carbon of the protonated acetaldehyde cation. This produces a 2-propanol radical cation and CO. Neutral 2-propanol is then obtained by recombination with a second electron. A mechanism involving ionisation-driven proton transfer is thus proposed as pathway to the formation of 2-propanol during electron exposure of condensed layers of acetaldehyde.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2016