Infrared cavity ringdown spectroscopy of the water cluster bending vibrations

We report the first measurement of water monomer bending vibrations in gase ous (H2O)(n) clusters. Infrared cavity ringdown spectroscopy reveals discre te and sequentially blue-shifted bands near 6 mu m for n = 2-4 and unresolv ed broad features for n > 4, supporting both theoretical predictions and so lid-state spectroscopy results. These measurements provide a measure of the monomer distortion that accompanies sequential hydrogen bond formation, wh ich will be valuable for the construction of potential energy surfaces for describing water.