Dissociative electron attachment and anion-induced dimerization in pyruvic acid

Abstract

We report partial cross sections for the dissociative electron attachment to pyruvic acid. A rich fragmentation dynamics is observed. Electronic structure calculations facilitate the identification of complex rearrangement reactions that occur during the dissociation. Furthermore, a number of fragment anions produced at electron energies close to 0 eV are observed, that cannot originate from single electron-molecule collisions. We ascribe their production to secondary reactions of the transient anions with neutral molecules. Such reactions turn out to be unusually efficient; the most probable reason for this is that they proceed via the formation of a double-hydrogen-bonded complex followed by an ultrafast proton transfer between the reaction partners.

Electron‐Induced Reactions in 3‐Bromopyruvic Acid

“…[11] Zawadzki et al observed anion-molecule reactions in as imilar crossed-beam quadrupole mass spectrometer arrangement to that used herein, in which the pressure wasb etween one and two orders of magnitude higher,b ut also in aD EA time-of-flightm ass spectrometer,i n which considerably lower pressures had to be used due to the multi-channel plate detector present in the chamber. [11] Zawadzki et al observed anion-molecule reactions in as imilar crossed-beam quadrupole mass spectrometer arrangement to that used herein, in which the pressure wasb etween one and two orders of magnitude higher,b ut also in aD EA time-of-flightm ass spectrometer,i n which considerably lower pressures had to be used due to the multi-channel plate detector present in the chamber.…”

“…Nevertheless,t his fragment is only detected in DEA to 3BP.Avibronic (non-adiabatic) coupling between the n!p*( involving the Br lone pair) and p!p*s tates is possible because the energies are very close to each other.T he fragment ions HCOO À ,O À and OH À are also formed through core excited resonances peaking at around5eV.T hese fragments are also observed in DEA to pyruvic acid, [11] and therefore, can be associated with transitions from the oxygen lone pair or p orbitals. However,a ccording to calculations, the n!p*t ransition is essentially dark due to an egligible oscillator strength.…”

“…[11] As generally expected for molecules containing ac arboxyl group, the most favourable hydrogen-bonded dimer structure was assumed to be ah ead-to-head configuration of the carboxyl groups. [11],t he cross-section for collision between the TNI and neutral species strongly depends on long-range interactions, which are dominated by anion-permanent dipole interactions in this case. However,i no ur experiments, we did not observe any signature of anion-induced dimerisation.…”

“…[11] Apart from the dehydrogenated parent anion, all fragment anions form only at electron energies of > 2eV. [11] Apart from the dehydrogenated parent anion, all fragment anions form only at electron energies of > 2eV.…”

“…[25] For 3BP,s uch ad imer configurationw ould be sterically possible because the bromine group is present at the opposite methyl group. [11] was stabilisation by ad ouble hydrogen bond in the dimer,i .e. Wep ostulate that this absence does not arise from specific experimental conditions.…”