The excited state dynamics of protonated aromatic aminoacids is quite complex and very rich: many fragmentation channels with reaction dynamics occurring on more than 10 orders of magnitude, from femtoseconds to seconds. The electronic spectroscopy in a large spectral domain brings new information on this complex behavior. The comparison with simple aromatic amines (aniline, benzylethylamine) also brings a new insight on the fragmentation mechanism. Experimentally, protonated aminoacids are produced in an electrospray source. They are further stored in a cryogenically cooled quadrupole trap and photo-dissociated by an OPO laser beam. The ionic photofragments are detected in a Time-Of-Flight mass spectrometer. The results are interpreted using high level ab-initio calculations. The experimental observations can be rationalized with a simple qualitative model, the ??*/?s* model1, which predicts that the excited state dynamics is controlled by the crossing between the ??* excited state and a ?s* state repulsive along the XH (X being O or N) coordinate. This leads to proton/hydrogen transfer from the protonated amino group toward the nearest neighbors, either the carbonyl group or the aromatic ring, and the subsequent dynamics and fragmentation is totally controlled by this first step.

Intramolecular excited state proton transfer: The key to photon induced dynamics in protonated aminoacids

248th National Meeting (2014)

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