Hydrogen bond breaking dynamics in the water pentamer: Terahertz VRT spectroscopy of a 20 μm libration

Hydrogen bonds in solid and liquid water are formed and broken via librational vibrations, hence characterizing the details of these motions is vital to understanding these important dynamics. Here we report the measurement and assignment of 875 transitions comprising 6 subbands originating from out-of-plane librational transitions of the water pentamer-d(10) near 512 cm(-1). The precisely measured (ca. 1 ppm) transitions reveal bifurcation splittings of similar to 1884 MHz, a similar to 4000 x enhancement over ground state splittings and 100 x greater than predicted by theory. The pentamer is thus the third water cluster to display greatly enhanced bifurcation tunneling upon single quantum excitation of librational vibrations. From the intensity pattern of the observed transitions, the mechanism of bifurcation is established by comparison with theoretical predictions. Published by AIP Publishing.