Determination of Carbide, Carbyne, and Carbene Bond Energies by Gas-Phase Photodissociation of RhCH₂⁺, NbCH₂⁺, and LaCH₂⁺

Three photoproducts, MCH⁺, MC⁺, and M⁺, are observed in the photodissociation of MCH₂⁺ (M = Rh, Nb, and La). In contrast, the low-energy collision-induced dissociation of RhCH₂⁺ and NbCH₂⁺ yields MC⁺ and M⁺ whereas LaCH₂⁺ produces only La⁺. Each photodissociation spectrum reveals two peaks: 240 nm (α = 0.06 A²) and 280 nm for RhCH₂⁺, 240 nm (a = 0.20 A²) and 390 nm for NbCH₂⁺, and 260 nm (α = 0.19 A²) and 320 nm for LaCH₂⁺Photoappearance thresholds for the products yield bond energies for M⁺-CH₂, M⁺-CH, and M⁺-C for each metal ion. Ionization potentials for RhC, NbC, and LaC are calculated on the basis of Z)°(M-C) and Z)°(M⁺-C). Plots of metal-ion ligand bond energies vs. bond energies for corresponding carbon analogues show linear correlation and allow bond order predictions to be made for the metal complexes.