Ion-molecule clustering thermochemistry by laser ionization high-pressure mass spectrometry

A laser ionization source has been developed and applied to measure the equilibrium thermochemistry of the clustering of neutral molecules with atomic metal ions. This high-pressure mass spectrometric method enables cluster association reactions to be studied at pressures that ensure both atomic ion thermalization and collisional stabilization of the nascent cluster ions. Initial application to the thermochemical properties of the association reactions of Cu⁺ with Kr, N₂ (up to five molecules), H₂O, CH₃OH, and CH₃COCH₃ is described. The binding energies for Cu⁺·Kr and Cu⁺·N₂ are similar to the analogous Na⁺ complexes, as expected from predominantly electrostatic interactions. The binding energies show reasonable variations with the proton affinity of the molecule.