Crystal-field effects in hexagonal closed-packed molecular $\mathrm{H}{}_2$ and $\mathrm{D}{}_2$ are examined over a broad range of pressures. The lattice distortion parameter (the deviation of the $c/a$ ratio from the ideal value 1.633), orientational order parameter, and crystal-field parameter in hexagonal close-packed (hcp) structures of $p\text{−}\mathrm{H}{}_2$, $o\text{−}\mathrm{D}{}_2$, and $n\text{−}\mathrm{H}{}_2$ are calculated using the semiempirical lattice-dynamic approach. It is shown that the lattice distortion in the $J$-even species is two order of magnitude smaller compared with that found in $n\text{−}\mathrm{H}{}_2$ and $n\text{−}\mathrm{D}{}_2$. The difference is due to splitting of the $J$-odd rotational levels in the $J$-even/$J$-odd mixtures.

• Received 31 March 2014

DOI:https://doi.org/10.1103/PhysRevB.90.024501