Electron attachment to CCl₃COOH molecule and clusters

Abstract Trichloroacetic acid (TCA) is an integral part of the atmosphere as well as a prototypical small polyhalogenated organic acid. Here, we investigate dissociative electron attachment (DEA) to the TCA molecule and small (TCA) N clusters combining cluster beam experiments with quantum chemical calculations exploiting genetic algorithm search and structure clustering. We report negative ion mass spectra at electron energies of 2 eV and 6.8 eV as well as energy dependent ion yields from 2 eV to 10 eV. The chlorine anion Cl − formation is by far the dominating channel at all energies in both isolated molecule and clusters. The calculations suggest that the C–Cl bond breaks spontaneously in the ground state of the transient negative anion. For a single molecule, about an order of magnitude less abundant CCl <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> </mml:math> CCl 2 COO − , and CCl 3 COO − ions are observed. These ions correspond to the HCl + CO 2 , HCl, and H abstraction reactions, respectively. In the cluster environment, the major cluster ion fragments after the Cl − ion correspond to the H abstraction, with other fragmentation pathways (HCl abstraction) being strongly suppressed or not observed at all (HCl + CO 2 ). Our calculations substantiate the experimental observations and show how the hydrogen bond network efficiently controls the dissociation pathways in molecular clusters.