2012ApJ...749...67O

The present study experimentally demonstrated that solid H₂ O is formed through the surface reaction OH + H₂ at 10 K. This is the first experimental evidence of solid H₂ O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H₂ O 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.