Crystalline structures in large ammonia clusters studied by IR cavity ringdown spectroscopy and a density functional theory calculation

Abstract We observed the NH stretching vibrations of large ammonia clusters by IR cavity ringdown spectroscopy. The degenerate stretching vibration ( ν 3 ) showed an increase in the absorption intensity and a narrowing of the bandwidth with increasing cluster size. The calculated crystalline model clusters, (NH 3 ) n ( n  = 7, 19, and 31), revealed that the ν 3 vibrations of the interior and surface NH 3 molecules show blue- and red-shifts with increasing cluster size, respectively. These results suggest that the ν 3 frequencies in large clusters converge, and the observed ν 3 narrowing is ascribed to this convergence in the crystalline hydrogen bonded clusters.