Adsorbed carbon monoxide is utilized as a double layer probe molecule because of its strong absorption in infrared region and because of the high sensitivity of the carbon-oxygen bond to changes in the environment local to the electrode surface. Potential Difference Infrared Spectroscopy was used to investigate the structural behavior of CO adsorbed on a platinum electrode. Carbon monoxide was found to be exclusively linear-bonded on platinum electrode in the presence of tetra-n alkylammonium perchlorate/acetonitrile. No bridge-bonded species were observed. It was also found that the IR peak position of adsorbed CO is linearly dependent upon applied electrode potential, in agreement with Electrochemical Stark effect. The Stark tuning rate of adsorbed CO was determined to be inversely proportional to electrolyte cation size. This quantitative relationship between the Stark tuning rate and cation size is the first time that this has been experimentally demonstrated. Statistical treatment proved that surface coverage influences the rate of infrared peak position shift. The effect of surface coverage upon the conformation of tetra-n-octylammonium cation was also observed. Data suggested that tetra-n-octylammonium cation changes its conformation with surface coverage