Corannulene and its complex with water: a tiny cup of water.

We report the results of a broadband rotational spectroscopic study of corannulene, CH, all of its singly substituted C isotopologues, and a complex of corannulene with one molecule of water. Corannulene is a polycyclic aromatic hydrocarbon (PAH) with a curved structure that results in a large dipole moment. Observation of C isotopic species in natural abundance allowed us to precisely determine the molecular structure of corannulene. The differences between the experimental C-C bond lengths correlate to the double-bond character predicted using Kekule's resonance structures. In the case of CH-HO, the water molecule is found to reside inside the bowl-like structure of corannulene. Our experimental and theoretical results indicate that the water molecule rotates freely around its C axis and that dispersion interactions are the dominant contribution to the binding.