Infrared photodissociation spectroscopy of cold cationic trimethylamine complexes

Cryogenic ion-trap infrared photodissociation spectroscopy combined with a dielectric barrier discharge source was constructed to establish the general trends in the stepwise growth motif of trimethylamine (TMA)n+ complexes. The results showed a strong preference for the formation of a stable charge-shared NN type (TMA)2+ ion core over the proton-transferred CHN type ion core, evidencing that the source condition has a remarkable effect on the kinetic stability of isomers. A maximum of four TMA molecules are located perpendicularly to the NN axis of the charge-shared (TMA)2+ ion core. In the n = 7 and 8 clusters, the subsequent two TMA molecules are located at each end of the NN axis of the (TMA)2+ ion core, completing the first coordination shell. Starting at n = 9, the additional TMA molecules form a second solvation shell, and the cluster spectra show similarities to the solution phase spectrum of aqueous TMA.