An infrared spectroscopic study Of CO2 that becomes permanently trapped in carbon nanotube bundles during thermolysis is reported. The temperature dependence of the nu(3) modes for trapped CO2 is studied with two-dimensional infrared correlation spectroscopy. Computer simulations are used to extract the basic physics of trapped CO2 and to make qualitative connections with changes seen in the infrared spectra. Experimental and simulated CO2 adsorption studies point to a sequential filling of adsorption sites in opened nanotubes with interstitial sites preceding endohedral sites. The limited number of sites available to the trapped CO2 species is used to facilitate a tentative assignment of vibrational peaks to specific sites in the nanotube bundles.