Collision-Induced Dissociation and Theoretical Studies of Na⁺−Acetonitrile Complexes

Collision-induced dissociation of Na⁺(CH₃CN)_x, x = 1−5, with xenon is studied as a function of kinetic energy using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed is endothermic loss of one acetonitrile molecule. The cross section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and dissociation lifetimes. Ab initio and density functional calculations at the MP2(full)/6-31G* and B3LYP/6-31G* levels of theory are used to determine the structures of these complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical bond dissociation energies are determined from single point calculations at the MP2(full)/6-311+G(2d,2p) and B3LYP/6-311+G(2d,2p) levels using the MP2(full)/6-31G* and B3LYP/6-31G* optimized geometries, respectively. The experimental bond energies determined here are in good agreement with previous experimental measurements for all complexes. Good agreement between theory and experiment is also found for all clusters except x = 5, where it is apparent that more basis functions are necessary to adequately describe the very weak noncovalent interactions in this complex.