Formation and Decay of the Dehydrogenated Parent Anion upon Electron Attachment to Dialanine

ABSTRACT: The dehydrogenated parent anion [M−H](−) is one of the most dominant anions formed in dissociative electron attachment to various small biomolecules like nucleobases and single amino acids. In the present study, we investigate the [M−H](−) channel for the dipeptide dialanine by utilizing an electron monochromator and a two-sector-field mass spectrometer. At electron energies below 2 eV, the measured high-resolution ion-efficiency curve has a different shape to that for the single amino acid alanine, which is explained by the altered threshold energies for formation of [M−H](−) determined in quantum chemical calculations. Moreover, the structure of the formed [M−H](−) anion is further studied by investigating the unimolecular and collision-induced decay of this anion. Trajectory calculations have been carried out to aid the interpretation of the experimentally observed fragmentation patterns.