Infrared spectra have been obtained for the liner and T?shaped isomers of CO2–HCN using the optothermal detection method. These spectra correspond to the intramolecular C–H stretching vibration in each isomer. The infrared results are consistent with the structures determined previously from microwave spectroscopy and provide additional data that is helpful in making meaningful comparisons with theory. A b i n i t i o calculations have also been carried out for this system using three different basis sets. The agreement between the experimental and calculated structures is good for all three basis sets, while the vibrational frequency shifts (scaled to the monomer) and the intermolecular stretching force constants are much more basis set dependent. Nevertheless, the overall agreement between experiment and a b i n i t i o theory is very good.
