Structures of α-Type Ions Formed in the 157 nm Photodissociation of Singly-Charged Peptide Ions

One hundred fifty-seven nm photodissociation of singly-charged peptide ions induces the cleavage of α-carbon to carbonyl-carbon bonds along the backbone. an + 1 radical ions are observed as the primary photolysis products of peptides with N-terminal arginines in a linear ion trap mass spectrometer. The radical elimination pathways undertaken by the an + 1 radical ions to form more stable even-electron species are studied in hydrogen-deuterium (H/D) exchange experiments. Two types of an ions along with d-type ions are observed as secondary elimination products. The relative abundance of each depends on the C-terminal residue of the radical fragment ion.