Chemical reactions in clusters of trifluoroacetic acid (CF3COOH) triggered by electrons at sub-excitation energy (<2Â eV)

Low energy (<2 eV) electron attachment to clusters of trifluoroacetic acid (CF3COOH) generates a variety of negatively charged complexes. They are formed via intracluster dissociative electron attachment (DEA) leading to solvated fragment ions, and (evaporative) associative electron attachment resulting in non-decomposed cluster ions including the monomer. The most intense signal is observed at 131 amu and is assigned to the ion-molecule complex CF3COO−·H2O. It is the result of a chemical reaction initiated by the attachment of electrons at an energy of 0.4 eV to the neutral hydrogen bonded dimer. This reaction exhibits a remarkable size selectivity as it is virtually restricted to the dimer. An alternate pathway, namely expulsion of the neutral water molecule from the negatively charged dimer, thereby forming the anhydride of acetic acid, is also observed at comparatively weaker intensity. These assignments are supported by experiments with clusters of deuterated acetic acid (CF3COOD). Ion yield curves of different anionic complexes are also presented and discussed in relation to previous experiments on DEA to single CF3COOH molecules [J. Langer, M. Stano, S. Gohlke, V. Voltin, E. Illenberger, Phys. Chem. Lett., in press].