Infrared Spectroscopic Evidence for Protonated Water Clusters Forming Nanoscale Cages

Abstract
Size-dependent development of the hydrogen bond network structure in largesized clusters of protonated water, H + (H 2 O) n ( n = 4 to 27), was probed by infrared spectroscopy of OH stretches. Spectral changes with cluster size demonstrate that the chain structures at small sizes ( n ≲ 10) develop into two-dimensional net structures (∼10 < n < 21), and then into nanometer-scaled cages ( n ≥ 21).