Water-carbon disulfide dimers: observation of a new isomer and structure theory.

The weakly bound dimer water-carbon disulfide is studied by structure theory and high-resolution infrared spectroscopy. The calculations yield three stable minima in the potential energy surface, all planar. The most stable, isomer 1, was observed previously by microwave spectroscopy. It has symmetry, an S-O bond, and a linear O-S-C-S backbone. Isomer 2, the next most stable, has not been considered previously by theory or experiment. It also has symmetry, but with a side-by-side structure. Isomer 3, which is slightly less stable, is side-by-side with one O-H bond pointing toward an S atom. The first gas phase water-CS infrared spectra are reported. For isomer 1, HO-, HDO-, and DO-CS are observed in the CS + region, HO-CS in the HO bend region, and DO-CS in the DO and stretch regions. The latter spectrum enables an experimental determination of the rotational parameter, which turns out to be larger than expected. The new isomer 2 is observed by means of a band in the HO region, confirming its symmetry and calculated structure.