Measurement of the ν8 intermolecular vibration of (D2O)2 by tunable far infrared laser spectroscopy

Abstract

The first accurate measurement of an intermolecular vibration of the water dimer is reported. Five vibration–rotation-tunneling (VRT) bands of the perdeuterated isotope, located near 84 cm−1, have been assigned to the A1/E/B1 tunneling components of the Ka=0←0 and Ka=1←0 subbands. The vibration involves large amplitude motion of the hydrogen bond acceptor and is assigned as the ν8 acceptor wag. The spectra indicate strong coupling of both the donor–acceptor interconversion and donor tunneling motions to the excited vibrational coordinate. This measurement provides a benchmark for future efforts toward the determination of an accurate potential energy surface for the water dimer.