Water Formation through a Quantum Tunneling Surface Reaction, OH + H2,   at 10 K
  The present study experimentally demonstrated that solid H2O is formed through the surface reaction OH + H2 at 10 K. This is the first experimental evidence of solid H2O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H2O formation through the reaction OH + H2 is about one order of magnitude more effective than HDO formation through the reaction OH + D2. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling. 
Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, and A. Kouchi
astro-ph.GA physics.chem-ph