Collision-Induced Dissociation and Theoretical Studies of Mg⁺ Complexes with CO, CO₂, NH₃, CH₄, CH₃OH, and C₆H₆

Abstract

The sequential bond energies for complexes of Mg + with CO, CO 2, NH 3, CH 4, CH 3 OH, and C 6 H 6 are determined by collision-induced dissociation (CID) with xenon or argon in a guided ion beam tandem mass spectrometer. The kinetic energy dependence of the CID and ligand exchange cross sections are analyzed to yield 0 and 298 K bond energies for Mg + −L after accounting for the effects of multiple ion−molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. Bond energies (in eV) to Mg + at 0 K are determined for L = Ar (0.10 ± 0.07), Xe (0.32 ± 0.12), 1−2 CO (0.43 ± 0.06 and 0.40 ± 0.03), 1−3 CO 2 (0.60 ± 0.06, 0.50 ± 0.03, and 0.46 ± 0.06), 1−5 NH 3 (1.60 ± 0.12, 1.27 ± 0.07, 0.99 ± 0.09, 0.45 ± 0.11, and 0.58 ± 0.12), 1−2 CH 4 (0.29 ± 0.07 and 0.15 ± 0.07), 1−3 CH 3 OH (1.51 ± 0.07, 1.25 ± 0.07, and 0.95 ± 0.09), and one C 6 H 6 (1.39 ± 0.10 eV). As expected for largely electrostatic interactions, the sequential bond energies generally decrease monotonically with increasing number of ligands. These values are in good agreement with theoretical values in the literature and ab initio calculations performed here, but the agreement is mixed for comparison with results of photodissociation measurements. Qualitatively, geometries of these complexes are controlled by interactions of the ligands with the single polarized valence electron on Mg + .