Processes induced by the attachment of slow electrons to formic acid and its hydrogen-bonded dimer were studied. The elastic cross section and the cross section for the excitation of low quanta of discrete vibrations were found to be of a similar magnitude for both targets. A dramatic difference was found in the excitation of a vibrational quasicontinuum in the 1–2 eV range with the ejection of very slow electrons ($E<0.1\mathrm{eV}$), which was about $20\times$ more intense in the dimer. The association of two formic acid molecules to form a dimer thus dramatically increases the power to quasithermalize electrons arriving with energies in the 1–2 eV energy range. Rapid electron-driven intracluster proton transfer is invoked to explain the observation.

• Received 22 November 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.123201