We are investigating certain chabazite zeolite-type materials which have unusual structural features that allow the extra-framework cations to act as molecular trapdoors. These materials can therefore selectively allow certain gases access to the internal pores of the zeolite while excluding others, making them promising candidates for application in gas separation and sequestration and isotope separations. We will collect powder neutron diffraction data from samples of trapdoor Cs-chabazite and K-chabazite (variants with tailored selectivity for CO2 over CH4 and D2 over H2, respectively) above and below the transition temperature for gate opening. We will also monitor changes in cation site occupancy via sequential refinement of a series of 10 min data sets to extract kinetic data. Full analysis of the data from these experiments will then allow a full structural description of small molecule interactions in chabazite zeolites, which will aid the design of new molecular trapdoor materials for improved adsorption and separation.