The next step in microsolvation of water by CO2: study of water-(CO2)3 by quantum chemistry calculations and combined microwave and infrared spectroscopy.

As a probe of the initial stages of the solvation of H2O in CO2, high resolution spectra of water-(CO2)3 clusters are observed using supersonic jet expansions with a chirped-pulse Fourier transform microwave and a tunable infrared laser spectrometer. The microwave results in the 2-18 GHz range give precise descriptions of the rotational levels in the ground vibrational states of H2O-(CO2)3, D2O-(CO2)3, and two forms of HDO-(CO2)3. The infrared results in the CO2ν3 region (≈ 2350 cm-1) include two of the three possible fundamental modes for D2O-(CO2)3 as well as the stronger of these for H2O-(CO2)3 and D2O-(13CO2)3. Density functional theory structural calculations agree very well with the observed spectra. This structure has no symmetry elements and is not particularly obvious a priori.