Dissociation activation barrier and heat of chemisorption: A morse-type analytical approach

The activation barrier ΔE¹_ABfor dissociation AB → A + B on transition-metal surfaces is analyzed within an additive Morse-type approach based on the bond-order conservation. It is shown that $\text{Δ}\text{E}{}^1{}_{\mathrm{AB}}\text{=}\text{D}{}_{\mathrm{AB}}\text{?(}\text{Q}{}_{\mathrm{A}}\text{+}\text{Q}{}_{\mathrm{B}}\text{+}\text{Q}{}_{\mathrm{A}}\text{Q}{}_{\mathrm{B}}\text{/(}\text{Q}{}_{\mathrm{A}}\text{+}\text{Q}{}_{\mathrm{B}}\text{)}$ where D_AB is the gas-phase dissociation energy and Q_A(Q_B) is the heat of atomic chemisorption. Estimates of $\text{Δ}\text{E}{}^1\text{for H}{}_2\text{, N}{}_2\text{, O}{}_2$, and NO are shown to be in reasonable agreement with experiment. The two-dimensional potential diagram of the metal-AB interactions is defined analytically and discussed in some detail.