Orientational Phase Transition in the System Pyridine/Ag(111): A Near-Edge X-Ray-Absorption Fine-Structure Study

Abstract

A phase transition has been observed in the system pyridine adsorbed on Ag(111) at 100 K by near-edge x-ray-absorption fine-structure measurements in real time. At low pyridine coverages an angle between the ring plane and the surface plane of 45\ifmmode^\circ\else\textdegree\fi{} \ifmmode\pm\else\textpm\fi{}5\ifmmode^\circ\else\textdegree\fi{} was observed. This phase converts sharply at a submonolayer coverage to a phase with an angle between the ring plane and the surface plane of 70\ifmmode^\circ\else\textdegree\fi{} \ifmmode\pm\else\textpm\fi{}5\ifmmode^\circ\else\textdegree\fi{}. Continued exposure gradually leads to a randomly oriented multilayer.