A search for precursor states to molecular nitrogen chemisorption on Ni(100), Re(0001) and W(100) surfaces at ∼ 20 K

Abstract

We have studied adsorption and condensation of molecular nitrogen on Ni(100), Re(0001) and W(100) surfaces by XPS at surface temperatures ⩾ 20 K in order to search for a precursor state to the linearly bonded chemisorbed state (γ-state). Our data however show XPS spectra only from γ-N 2 at low exposures and from physisorbed and condensed N 2 at higher exposures. No intrinsic precursor is found, allowing an upper bound of approximately 3 kJ/mol to be placed on the activation barrier between any such state and the chemisorbed state. The physisorbed N 2 observed on top of γ-N 2 covered patches acts as an extrinsic precursor to chemisorption.