Abstract Nearly three decades have passed since Eischens et al. 1 measured the infrared bands of CO chemisorbed on Cu, Ni, Pt and Pd, and their assignments, unscathed by time and criticism, have prompted a great deal of infrared work on the interactions of CO with a wide variety of adsorbents. CO adsorption, followed by a variety of infrared techniques, has now become a valued conventional tool for surface studies. The C-O stretching bands of chemisorbed CO yield data about band frequency, half-width, contour and intensity, as well as band shifts and intensity changes when some parameter is changed, which provide information about the structure of the chemisorbed species and permit deductions to be made concerning the adsorbate-adsorbent interaction and the nature and properties of the surface. However, we now find and show that under certain conditions such data, measured by the conventional transmission/absorption (T/A) techniques, can be susceptible to errors and artifacts stemming from the measurement...