Low energy electron driven reactions in single formic acid molecules (HCOOH) and their homogeneous clusters

Low energy (0-3 eV) electron attachment to single formic acid (FA) and FA clusters is studied in crossed electron/molecular beam experiments. Single FA molecules undergo hydrogen abstraction via dissociative electron attachment (DEA) thereby forming HCOO(-) within a low energy resonance peaking at 1.25 eV. Experiments on the isotopomers HCOOD and DCOOH demonstrate that H/D abstraction occurs at the O-H/O-D site. In clusters, electron attachment is strongly enhanced leading to a variety of negatively charged complexes with the dimer M2(-) (M[triple bond]HCOOH) and its dehydrogenated form M (M-H)(-) as the most abundant ones. Apart from the homologous series containing the non-dissociated (Mn(-)) and dehydrogenated complexes (M(n-1) (M-H)(-), n > or = 1) further products are observed indicating that electron attachment at sub-excitation energies (approximately 1 eV) can trigger a variety of chemical reactions. Among these we detect the complex H2O (M-H)(-) which is interpreted to arise from a reaction initiated in the cyclic hydrogen bonded dimer target. In competition to hydrogen abstraction yielding the dehydrogenated complex M (M-H)(-) the abstracted hydrogen atom can react with the opposite FA molecule forming H2O and HCO with the polar water molecule attached to the closed shell HCOO(-) ion. The FA dimer can thus be used as a model system to study the response of a hydrogen bridge towards dehydrogenation in DEA.