- In laser desorption of a series of cyclically 9-substituted adenines, followed by multiphoton ionization, we observed characteristic fragmentation. This is in marked contrast to laser desorption under identical conditions of cyclically 9-substituted guanines, for which we obtained predominantly the parent mass. By applying resonant 2 photon ionization spectroscopy (R2PI) to the laser-desorbed, jet-cooled fragments, we show that the fragmentation is induced by the desorption process and not by the excitation/ionization process. Fragmentation takes place between C′2 and C′3 and between C′1 and O6 in the sugar ring. By adding a propyl bridge between C′2 and C′3, the fragmentation pathway changes to a cleavage of the C′4C′5 bond in the sugar ring. This allowed us to record R2PI spectra of a fragment species that can serve as a model for adenosine.