Diffusion of N-2 in ice crystal has been found from Raman scattering of the natural ice from the Antarctic ice sheet. In order to investigate the diffusion mechanism, we perform molecular dynamics simulations of diffusion of N-2 in ice. The results show that the N-2 molecule hops in the crystal by breaking hydrogen bonds in the ice lattice. The diffusion velocity with the mechanism is few orders larger than the estimate under the assumption of the interstitial mechanism. We conclude that the localized vibrational motion of N-2 is the dominant factor governing the diffusion mechanism. (C) 2004 Elsevier B.V. All rights reserved.