Low-Energy Electron Interactions with Methyl-p-benzoquinone: A Study of Negative Ion Formation

Methyl-p-benzoquinone (MpBQ, CH3C6H3(O)2) is a prototypical molecule
in the study
of quinones, which are compounds of relevance in biology and several
redox reactions. Understanding the electron attachment properties
of MpBQ and its ability to form anions is crucial in elucidating its
role in these reactions. In this study, we investigate electron attachment
to MpBQ employing a crossed electron-molecular beam experiment in
the electron energy range of approximately 0 to 12 eV, as well as
theoretical approaches using quantum chemical and electron scattering
calculations. Six anionic species were identified: C7H6O2–, C7H5O2–, C6H5O–, C4HO–, C2H2–, and O–. The parent
anion is formed most efficiently, with large cross sections, through
two resonances at electron energies between 1 and 2 eV. Potential
reaction pathways for all negative ions observed are explored, and
the experimental appearance energies are compared with calculated
thermochemical thresholds. Although exhibiting similar electron attachment
properties to pBQ, MpBQ’s additional methyl group introduces
entirely new dissociative reactions, while quenching others, underscoring
its distinctive chemical behavior.