Photodissociation of singly charged oligonucleotide cations: Arrhenius parameters and identification of nonstatistical processes

The lifetimes of singly charged protonated oligonucleotide cations, d (A)2, d (A)3, d (A)4, and d (A)5, were measured after UV photoabsorption in a storage ring. Two lifetime components were observed for d (A)3, d (A)4, and d (A)5 but only one for d (A)2. Assuming that the major fragmentation channel is the same for all oligonucleotide cations, namely loss of a protonated adenine base, with similar Arrhenius parameters, then the lifetimes are a result of different final temperatures after photon absorption. Such an analysis provides an activation energy Ea of 0.88 eV and preexponential factor A of 1010.2 s-1. Nonstatistical fragmentation was an important channel for all of the oligonucleotide cations, but most so for d (A)2, the one with the lowest number of neutral adenines.