The internal stretch of on-top-bonded CO on W(100) is monitored as a function of exposure at 90 and 295 K. At both temperatures significant population of this state (α-CO) occurs after the local adsorption of another coexisting state. The inhomogeneity of this coexisting state is reflected in the width of the α-CO internal stretch: higher adsorption and/or anneal temperatures produce more order in the coadsorbate. It is suggested that at 90 K the coexisting species largely consists of an extremely disordered weakened bond molecular state adsorbed parallel or nearly parallel to the surface. Two α-CO states are identified for adsorption at 295 K, confirming the earlier deduction from electron-stimulated desorption data.