Far-Infrared Investigation of the Benzene-Water Complex: The Identification of Large-Amplitude Motion and Tunneling Pathways.

The far-infrared spectrum of the weakly OH···π hydrogen-bonded benzene-water complex has been studied in neon and argon matrices, below 30 K. The in-plane water libration has been observed in both neon and argon for H2O and D2O complexed with C6H6 and C6D6 but not for the corresponding complexes involving HDO. Both H2O and D2O can tunnel between the two possible hydrogen bonds. This is not possible for HDO. The reported far-infrared observations have implications for the interpretation of the previously obtained molecular beam microwave spectrum of the benzene-water complex.