Structure of solid formamide at 7 K

The structure of formamide was redetermined at 7 K using neutron powder profile analysis. The space group is P21/n with a=3·5432(2), b=8·9512(5), c=6·9741(4) Å and β=101·051°. The results are in agreement with earlier X-ray results but a more accurate determination of the hydrogen positions has been made and a lower temperature has reduced anharmonic effects. A simple model using standard exp-6 atom-atom potentials, experimentally determined atomic charges and an exponential attractive potential for the O-D hydrogen bonds gives a good fit to the structural parameters.