Infrared spectroscopic experiments were performed to ascertain the mechanisms of molecular contaminant film removal with a carbon dioxide (CO2) gas/solid jet spray. In the jet spray nozzle, liquid CO2expands through an orifice and forms a spray of submillimeter‐sized solid particles entrained in a gas stream. This spray has been shown to be effective in removing particles and some molecular contaminant films. It has been hypothesized that the spray removes films by one of three methods: abrasion by the solid particles, thermal shock of the film, or formation of a transient liquid film into which the film dissolves, and which then resolidifies and scatters from the surface. We have compared the jet spray removal efficiency of contaminant films of varying solubility in CO2and measured in real time the cleaning rates of the jet spray for these films. The infrared spectroscopic data show strong correlations between film removal efficiency, the time required to remove a film, and the solubility of the film in liquid CO2. These data, combined with visual observations, indicate that the CO2jet spray cleaning occurs in two regimes. First, bulk film removal may occur via either thermal shock or abrasion. Second, the residual contaminant film is removed via solvation into the transient liquid CO2film formed by the impacting CO2particles. Not all contaminant films can be removed by this technique. Thick films that formed droplets could not be removed by the spray; the drops were simply moved around on the surface. Thin films that were not sufficiently soluble in CO2were not removed either. These results allow prediction of the jet spray removal efficiency based on identification of the contaminants.