We observed the NH stretching vibrations of large ammonia clusters by IR cavity ringdown spectroscopy. The degenerate stretching vibration (v(3)) showed an increase in the absorption intensity and a narrowing of the bandwidth with increasing cluster size. The calculated crystalline model clusters, (NH3)(n) (n = 7, 19, and 31), revealed that the v(3) vibrations of the interior and surface NH3 molecules show blue- and red-shifts with increasing cluster size, respectively. These results suggest that the v(3) frequencies in large clusters converge, and the observed v(3) narrowing is ascribed to this convergence in the crystalline hydrogen bonded clusters. (C) 2010 Elsevier B.V. All rights reserved.