Knowledge Bank

The dangling-OH groups at the surface of microporous amorphous ice bear a significant resemblance to the unbonded OH groups of the acceptor water molecule in the water dimer. Thus, the dimer can be used to gain insight into the behavior of the surface HOD molecules of amorphous ice, Several results have been reported that show the preference for D-bonding over H-bonding within water $dimers.1\&2$ It has been found that the H-boned dimers of HOD are approximately $60cm-1$ less stable than the D-bonded dimers. Only about 1% D-bonded HOD is present at 20K, but this increased to 3, 9, & 15% at 25, 33, & 50K, $respectively.1$ The deposition of HOD at 20K forms an amorphous deposit with nearly statistical distribution of the HOD surface orientation. During warming, this distribution is preserved until 50K where a shift to preferential D-bonding is observed. This shift coincides with the activation of the 3-coord dangling groups. Once past this preferential reorientation, this new distribution is preserved until the dangling groups are eliminated.