Two‐Dimensional Phase Transitions and Correlation Field Splitting in Unimolecular Layers of CO Physisorbed on NaCI(100) as Detected by Polarization Fourier‐Transform IR Spectroscopy

Abstract

AbstractA phase transition in the monolayer CO physisorbed on NaCI(100) was observed by means of polarization Fourier‐transform infrared spectroscopy. Above 35 K the spectra are in concert with molecules oriented perpendicularly to the surface, the unit cell being of p(1 × 1) symmetry. Below 35 K the molecules tilt, and a correlation field splitting appears. In this temperature range the spectra are in accordance with a p(2 × 1) structure with two equivalent molecules per unit cell, which are connected by a glide plane. Submonolayer spectra indicate random distribution of perpendicularly oriented CO molecules above 35 K, while at temperatures below 35 K ordered islands are formed.