Raman spectroscopic evidence for cooperative C-H...O interactions in the acetaldehyde-CO2 complex.

In carbonyl compounds having a hydrogen atom attached to the alpha-carbon or directly to the carbonyl carbon, our recent ab initio and solvation studies have predicted the presence of a weak C-H...O interaction with CO2. This intermolecular interaction acts cooperatively with the Lewis acid-Lewis base interaction that exists between CO2 and the carbonyl group. This communication provides the first experimental evidence for this cooperative interaction in the acetaldehyde-CO2 complex using Raman spectroscopy at 25.0 degrees C in the gas phase. The implications of these interactions in the solvation of carbonyl-based CO2-philes are also discussed.