02.04 FOCUS SESSION: Antimatter and electron collisionsDissociation dynamics of transient carboxylic acid anions formed by electron attachment

Simple carboxylic acids are well established to exhibit rich chemical reactivity in environments abundant in low energy free electrons. Dissociative electron attachment is an important reaction that occurs by resonant electron-molecule interactions, producing a transient negative ion resonance. There are several prominent examples of molecules having several resonances, characterized as single-electron shape resonances, or excited resonances, where a target electron is excited in the electron attachment process, producing a correlated two-electron one-hole system that decays by autodetachment or dissociation. Feshbach resonances occur when the potential energy of the resonance is lower than the corresponding excited neutral molecule. This energetically forbids the resonance from decaying by single-electron autodetachment, thus enabling nuclear motion to proceed on femtosecond timescales, which in turn can permit dissociation to occur.

Acetic acid, isolated in the gas phase, produces many reactive species by dissociative electron attachment. Such reactions proceed via an electronic shape resonance at low attachment energies, or electronic Feshbach resonances at higher energies. In this work we focus on the rich information provided by the momentum of the H^- or D^- anions produced by breaking specific bonds, namely the hydroxyl (O-H or O-D) and and methyl (C-H or C-D) bonds. We make direct comparisons between a series of Feshbach resonances in the two simplest carboxylic acids, formic acid (Refs 1-2) and acetic acid, to understand the dynamics underlying anion and radical formation.