Radiative Association Kinetics and Binding Energies of Chromium Ions with Benzene and Benzene Derivatives

The radiative association reactions of gas-phase Cr⁺ with benzene and three of its methyl derivatives (toluene, p-xylene, and mesitylene) were studied in the Fourier-transform ion cyclotron resonance ion trap. Sequential formation of the monomer complexes and the sandwich dimer complexes was observed, and the kinetics were analyzed by a recently developed canonical transition-state theory approach to give estimates of the binding energies. The bond strength of Cr⁺−(C<INF>6</INF>H<INF>6</INF>) was assigned as 1.70 ± 0.15 eV, and the bond strengths increased slightly with increasing methyl substitution, reaching 2.0 eV for mesitylene. The bond strength for Cr⁺(C<INF>6</INF>H<INF>6</INF>)−(C<INF>6</INF>H<INF>6</INF>) was assigned as 2.2 ± 0.4 eV, with similar values (within large uncertainties) for the other sandwich complexes. The Cr⁺−(C<INF>6</INF>H<INF>6</INF>) value was in good agreement with the value from collision-induced dissociation, and a best value of 1.73 ± 0.10 eV for this bond strength is recommended.