Heat of molecular chemisorption from bond-order-conservation viewpoint: Why morse potentials are so efficient

Abstract

Our analytic Morse-potential model of chemisorption based on bond-order conservation [Surface Sci. 150 (1985) L115; 163 (1985) L730] has been extended to calculate the heat of chemisorption Q AZ of molecules AZ coordinated parallel to a metal surface, where A and Z may be either the same or different atoms or atomic groups (“quasiatoms”). Examples include O 2, CO, H 2CCH 2, HC≡CH, H 2CO, and (CH 3) 2CO, where comparisons with the perpendicular AZ coordinations, considered earlier, are also made. The projected qualitative trends and quantitative estimates are in agreement with (scarce) experiment. It is argued that, within the bond-order-conservation framework, the efficiency of Morse potentials to describe the energetics of various chemisorption phenomena ultimately originates from the zero-energy gap between the occupied and vacant parts of the metal band.