Photodetachment of deprotonated aromatic amino acids: stability of the dehydrogenated radical depends on the deprotonation site.

While aromatic amino acids in their deprotonated form have been well characterized by IR and photoelectron spectroscopies, no information is available on the neutral dehydrogenated radicals and, in particular, on their stability when the deprotonation site is changed. This is investigated by observing the neutral fragment issued from either simple photodetachment or dissociative photodetachment of the deprotonated aromatic amino acids phenylalanine, tyrosine, and tryptophan. We show that the dehydrogenated radicals of aromatic amino acids produced upon photodetachment of molecules deprotonated on the carbonyl group dissociate without barrier, leading to the formation of CO and a radical amine.