Linking Chemical Physics and Surface Science: Thermochemistry of Adsorbates from Purely Gas Phase Data

A scheme is presented for calculating the heats of formation of adsorbed species on metal surfaces using only two pieces of gas phase data, both of which are available from either theory or experiment. Using this quasiempirical valence bond (QVB) approach, heats of adsorption and adsorbate-surface bond strengths can be estimated, yielding predictions of surface thermochemistry and reaction mechanisms. The power of this method lies in its ability to predict heats of adsorption and formation of molecular fragments that do not readily desorb on their own (e.g. reactive radicals), and thus do not lend themselves to direct measurements of their heats of adsorption.