Interactions of limonene with the water dimer.

The interactions of two molecules of water with the terpene limonene are characterised by chirped-pulse Fourier transform microwave spectroscopy. Seven isomers of limonene-(H 2 O) 2 have been observed, and identified from the comparison of their experimental spectroscopic parameters with those predicted by computational methods. In all isomers a distorted water dimer binds to limonene through O-H⋯π and C-H⋯O interactions, and shows a strong preference for interacting with equatorial conformations of limonene. O-H⋯π hydrogen bonds to both endocyclic and exocyclic double bonds of limonene are established. In one of the isomers the water dimer forms a bridge between the endocyclic and exocyclic double bonds of limonene. Our results help advance our understanding of the interactions of water with atmospheric compounds.