The power of FTIR spectroscopy for understanding the structure of molecularly adsorbed CO2: from conventional analysis to isotopic approaches.

Understanding the structure of molecularly adsorbed CO2 remains a challenging problem. Infrared spectroscopy is one of the most widely used techniques for studying adsorbed CO2 and provides information on adsorption states and surface interactions. However, conventional FTIR analysis often yields only indirect evidence regarding adsorption geometry and site occupancy, and in many studies molecularly adsorbed CO2 is identified without detailed structural characterization. This Feature Article review illustrates how isotopic methodologies substantially enhance the structural information accessible by infrared spectroscopy. Particular attention is devoted to isotopic linkage isomerism, which enables direct discrimination between end-on and bridging adsorption geometries, and to isotopic approaches for identifying geminal and higher-order adsorption complexes. Together, these methods transform isotopic substitution from a simple assignment tool into a powerful approach for determining the structure and organization of molecularly adsorbed CO2. Future opportunities and possible extensions of these concepts to more complex adsorption systems are also discussed.