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Ion-Induced Dipole Interactions and Fragmentation Times : C$α$ -C$β$ Chromophore Bond Dissociation Channel

The fragmentation times corresponding to the loss of the chromophore (C$α$-- C$β$ bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (\textless{}20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the C$α$--C$β$ bond cleavage.