Neutron-diffraction study of polycrystalline ${\mathrm{H}}_2$S${\mathrm{O}}_4$ and ${\mathrm{H}}_2$Se${\mathrm{O}}_4$

Polycrystalline ${\mathrm{H}}_2$S${\mathrm{O}}_4$ and ${\mathrm{H}}_2$Se${\mathrm{O}}_4$ were studied by powder neutron-diffraction techniques at temperatures near the melting points and at 10 K. This work was undertaken to determine hydrogen positions and to search for order-disorder transitions in the hydrogen-bond networks. Rietveld refinement located the hydrogen positions and established that the hydrogen atoms are ordered at the temperatures studied (i.e., no ordering transitions). The other atom positions were found to be consistent with those determined in earlier x-ray single-crystal analyses of the ${\mathrm{H}}_2$S${\mathrm{O}}_4$ and ${\mathrm{H}}_2$Se${\mathrm{O}}_4$ crystal structures.