Sign of the Nuclear Quadrupole Interaction in Rhenium Metal

The sign and magnitude of the nuclear quadrupole splitting in rhenium metal have been determined by heat-capacity measurements down to 19 mK. We find an average coupling constant $\frac{e^2\mathrm{qQ}}{h}=-246\mathrm{}\pm 2$ MHz for the two rhenium isotopes. This gives an electric field gradient at the nucleus of $q=-100\mathrm{}{q}_{\mathrm{lat}}$, where $q_{\mathrm{lat}}$ is the source gradient produced by the ${\mathrm{Re}}^{7+}$ ion cores in the hcp lattice.