Experimental and theoretical studies of Co(CH₄)_x⁺ with x = 1-4

The sequential bond energies of Co(CH₄)_x⁺, x = 1-4, are determined experimentally and theoretically. Collision-induced dissociation studies conducted using a guided ion beam tandem mass spectrometer yield 0 K bond energies of D₀[Co⁺-Xe] = 0.85 ± 0.07 eV, D₀[Co⁺-CH₄] = 0.93 ± 0.06 eV, D₀[Co(CH₄)⁺-CH₄] = 1.00 ± 0.05 eV, D₀[Co(CH₄)₂⁺-CH₄] = 0.41 ± 0.05 eV, and D₀[Co(CH₄)₃⁺-CH₄] = 0.67 ± 0.06 eV. These numbers are in excellent agreement with ab initio calculations which lead to values of D_e[Co⁺-(CH₄)] = 0.93 eV, D_e[Co(CH₄)⁺-CH₄] = 1.00 eV, D_e[Co(CH₄)₂⁺-CH₄] ≈ 0.40 eV, and D_e[Co(CH₄)₃⁺-CH₄] ≈ 0.70 eV. We find that the nonmonotonic behavior in the sequential binding energies arises from changes in hybridization at the metal center as the third ligand is bound.