Infrared Spectra of the Water–CO2 Complex in the 4.3–3.6 μm Region and Determination of the Ground State Tunneling Splitting for HDO–CO2

Spectra of waterCO2 dimers are studied using a tunable mid-infrared source to probe a pulsed slit jet supersonic expansion. H2O–CO2 and D2O–CO2 are observed in the CO2 ν3 fundamental region (≈2350 cm–1), D2O–CO2 is also observed in the D2O ν3 fundamental region (≈2790 cm–1), and HDO–CO2 is observed in the HDO O–D stretch fundamental region (≈2720 cm–1), all for the first time in these regions. Analysis of the spectra yields excited state rotational parameters and vibrational shifts. They also yield the first experimental values of the ground state internal rotation tunneling splittings for D2O–CO2 (0.003 cm–1) and HDO–CO2 (0.0234 cm–1). The latter value is a direct determination made possible by the reduced symmetry of HDO–CO2. These results provide stringent and easily interpreted tests for theoretical water–CO2 potential energy surface calculations.