Hydrogen bonding, structure, and dynamics of benzonitrile–water

Rotational transitions with high quantum numbers J and K of the 1:1 complex of benzonitrile with H2O and D2O have been investigated in the frequency range 60–78 GHz with the free jet absorption microwave technique to get detailed information on the unusual hydrogen bond and on the dynamics of the large amplitude motions of the water moiety. With respect to previous microwave studies [V. Storm, D. Consalvo, and H. Dreizler, Z. Naturforsch. A 52, 293 (1997); R. M. Helm, H.-P. Vogel, H. J. Neusser, V. Storm, D. Consalvo, and H. Dreizler, 52, 655 (1997); V. Storm, H. Dreizler, and D. Consalvo, Chem. Phys. 239, 109 (1998)] the position of the water oxygen has been confirmed and the planar configuration of the complex has been determined. The distance of the oxygen atom to the ortho hydrogen is 2.48 Å, the angle to the ortho C–H bond is 144° and the angle between the free hydrogen atom of water with the same C–H bond is 164°. A coupled analysis of the 0+ and 0− states observed for the normal species was performed and the experimental data were reproduced by a flexible model which allowed the determination of the barrier to internal rotation of water [V2=287(20) cm−1] and the structural relaxation associated with the dynamic process.