Resonant Enhanced Multi-Photon Ionization (REMPI) mass spectroscopy is a powerful tool for the investigation of dynamic molecular states. The principles of REMPI as they relate to action mass spectroscopy are outlined. Two major investigations are presented. REMPI, in combination with quantum chemical theory, is used to study the mechanism of internal conversion in a family of related purines and pyrimidines. These same techniques are also used to study competition between hydrogen bonding and pi-stacking interactions in a set of non-standard nucleobases.
