Infrared spectrum of CO on NaCl(100)

Adsorbed molecules on alkali metal halide surfaces serve as model systems for the study of physisorption, two-dimensional phase transitions, vibrational relaxation, and surface chemistry. However, all previous optical spectroscopy of these substrates had used films rather than well-defined crystal faces. They report here, for the first time, the infrared spectrum of CO on the (100) face of NaCl. While the vibrational frequency matches that of CO on NaCl films, the bandwidth is much narrower. Polarization measurements show that CO is aligned perpendicular to the (100) face. The narrow and easily observed absorption features will make the infrared spectroscopy of adsorbed molecules a sensitive probe of alkali metal halide surface interactions.