Adsorbate ordering processes and infrared spectroscopy: An FT-IRAS study of N2 chemisorbed on the Ni(110) surface

Abstract

A newly constructed apparatus for Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) studies has been used in a detailed study of the N–N stretching band of N2 weakly chemisorbed on the Ni (110) surface. The high resolution and the high signal-to-noise ratios of the spectra allow observation of subtle changes of the band shape which accompany changes in the overlayer structure. The results are discussed with respect to a detailed two-dimensional phase diagram recently proposed for the N2/Ni (110) system. The IR data clearly reveal that for low coverages nonequilibrium adsorption occurs at 81 K, while equilibrium is attained at 125 K in agreement with the phase diagram. The present results indicate that the incommensurate overlayer structure which forms at the highest coverages is characterized by an intense sharp IR band at 2194 cm−1, a weak shoulder at 2204 cm−1, and a still weaker satellite peak at 2220 cm−1. The IR results for the incommensurate N2 overlayer are compared with models originally proposed to reconcile LEED and vibrational studies of incommensurate CO overlayers.