Formation of the Long-Lived Parent Anion upon Electron Attachment to Menadione

Menadione is a multifunctional molecule involved in critical biological processes such as blood coagulation, redox regulation, and cellular metabolism. Understanding its electron attachment properties and capacity to form stable anions is essential for elucidating its function in biological environments. In this study, we investigated electron attachment to menadione using a crossed electron-molecular beam experiment, complemented by quantum chemical and electron scattering calculations. Upon electron attachment, the efficient formation of the parent molecular anion is observed. Its signal extends from 0 to 2.5 eV, with pronounced peaks at ∼0 and 0.7 eV, assigned to the formation of different precursor anion states. Two fragment anions, namely, C₂H₂^- and CH₃^-, were also detected. In contrast to the parent anion, their formation occurs with significantly lower efficiency and only at higher electron energies, above 4 eV, consistent with the higher energy thresholds required for dissociative electron attachment. Our findings show, on the one hand, that the metastable parent anion of menadione has a relatively long lifetime, which may be further extended in biological environments due to solvent effects, and, on the other hand, that it is structurally stable in the interaction with low-energy electrons.