Photodissociation of S atom containing amino acid chromophores

Photodissociation of 3-(methylthio)propylamine and cysteamine, the chromophores of S atom containing amino acid methionine and cysteine, respectively, was studied separately in a molecular beam at 193nm using multimass ion imaging techniques. Four dissociation channels were observed for 3-(methylthio)propylamine, including (1) CH3SCH2CH2CH2NH2→CH3SCH2CH2CH2NH+H, (2) CH3SCH2CH2CH2NH2→CH3+SCH2CH2CH2NH2, (3) CH3SCH2CH2CH2NH2→CH3S+CH2CH2CH2NH2, and (4) CH3SCH2CH2CH2NH2→CH3SCH2+CH2CH2NH2. Two dissociation channels were observed from cysteamine, including (5) HSCH2CH2NH2→HS+CH2CH2NH2 and (6) HSCH2CH2NH2→HSCH2+CH2NH2. The photofragment translational energy distributions suggest that reaction (1) and parts of the reactions (2), (3), and (5) occur on the repulsive excited states. However, reaction (4) and (6) occur only after the internal conversion to the electronic ground state. Since the dissociation from an excited state with a repulsive potential energy surface is very fast, it would not be quenched completel...