Photodestruction of adenosine 5'-monophosphate (AMP) nucleotide ions in vacuo: statistical versus nonstatistical processes.

The lifetimes of both deprotonated adenosine 5(')-monophosphate (AMP) and protonated AMP, after 266-nm photon absorption and intramolecular vibrational redistribution, were determined to be 16 micros based on a newly developed heavy-ion storage ring technique. Protonation of the adenine nucleobase seriously affects the fragmentation mechanism: the major part of the photoexcited anions fragment in a statistical (ergodic) process, whereas nearly all the cations (>99%) fragment in a nonergodic process. In solution at natural pH the AMP anion is prevalent and photoproduct formation is therefore less important as the time for vibrational cooling is of the order of picoseconds.