An Absolute Sodium Cation Affinity Scale: Threshold Collision-Induced Dissociation Experiments and ab Initio Theory

Abstract

Threshold collision-induced dissociation of Na+(L) with xenon is studied using guided ion beam mass spectrometry. The ligand L includes ethene, benzene, phenol, ammonia, acetaldehyde, acetone, and N,N-dimethylformamide. In all cases, the primary product formed corresponds to endothermic loss of the neutral ligand and the only other product observed is the result of ligand exchange processes to form NaXe+. The cross-section thresholds are interpreted to yield 0 and 298 K bond energies for Na+−L after accounting for the effects of multiple ion−molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. Ab initio calculations at several levels of theory compare favorably to the experimentally determined bond energies for these and previously studied systems, L = Ar, CO, dimethyl ether, H2O, methylamine, imidazole, dimethoxyethane, and several alcohols. Combined, these ligands cover a very wide range in binding energies, and thereby help to establish an absolute scale for sodium cation affinities.