MEASUREMENT OF THE NU-8 INTERMOLECULAR VIBRATION OF (D2O)2 BY TUNABLE FAR INFRARED-LASER SPECTROSCOPY

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 K(a) = 0 <-- 0 and K(a) = 1 <-- 0 subbands. The vibration involves large amplitude motion of the hydrogen bond acceptor and is assigned as the nu(s) 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.