TERAHERTZ LASER VIBRATION-ROTATION-TUNNELING SPECTRUM OF THE WATER PENTAMER-D(10) - CONSTRAINTS ON THE BIFURCATION TUNNELING DYNAMICS

The vibration-rotation-tunneling (VRT) spectrum of a low-frequency int ermolecular vibration of(D2O)(5) was recorded near 0.9 THz (30.2 cm(-1 )). From an analysis of the relative intensities in the compact Q-bran ch region, the ground-state C-rotational constant is estimated to be 9 75 +/- 60 MHz, consistent with ab initio structural predictions. The p recisely determined B-rotational constant (B = 1750.96 +/- 0.20 MHz) a grees well with previous results. Efforts to resolve possible bifurcat ion tunneling fine structure, such as that observed in VRT spectra of (D2O)(3), revealed no such effects. This constrains the splittings to be less than 450 kHz, or roughly 3 times smaller than required by prev ious results. (C) 1998 Published by Elsevier Science B.V. All rights r eserved.