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 P2(1)/n with a = 3.5432(2), b = 8.9512(5), c = 6.9741(4) angstrom and beta = 101.051-degrees. 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.