QUANTIFYING HYDROGEN-BOND COOPERATIVITY IN WATER - VRT SPECTROSCOPY OF THE WATER TETRAMER

Measurement of the far-infrared vibration-rotation tunneling spectrum of the perdeuterated water tetramer is described, Precisely determined rotational constants and relative intensity measurements indicate a c yclic quasi-planar minimum energy structure, which is in agreement wit h recent ab initio calculations, The O-O separation deduced from the d ata indicates a rapid exponential convergence to the ordered bulk valu e with increasing cluster size. Observed quantum tunneling splittings are interpreted in terms of hydrogen bond rearrangements connecting tw o degenerate structures.