STABILITIES OF FAST-ATOM-BOMBARDMENT DESORBED ALKALI-METAL ADDUCTS OF PYRIMIDINE MOLECULES

A pyrimidine derivative has been used as a model compound to evaluate the relative stabilities of protonated and alkali cationized molecules formed via fast atom bombardment (liquid secondary ion mass spectrometry); stabilities are shown to increase with increasing alkali cation size. Relative abundances of daughter ions formed by competitive decompositions (losses of NH3, CH4) have been analyzed with respect to the initial internal energy content of protonated and cationized pyrimidine molecules. Comparisons are made of metastable and collisionally-activated decompositions, and of unimolecular decompositions over the course of liquid matrix depeletion. Relative activation energies and frequency factors for ammonia and methane eliminations have been qualitatively assessed. The mechanism for ammonia loss is discussed in the light of results obtained from deuterium labeling of mobile protons. © 1990.