Slope anomaly in the vapour pressure curve of Hg
The investigation of normally-metallic fluids at reduced densities has created considerable experimental and theoretical interest. Hensel1 has presented evidence for transitions, related to electronic properties, in both the liquid and vapour phases of Hg, and predicted that these would affect the liquid–vapour transition. We present here evidence that the vapour pressure curve of Hg, p(T), has an unusual and probably unique form in that the In p against 1/T plot showed a sharp change of slope at temperature T = T′ = 1,361 K and saturated liquid density ρL = 10.7 g cm−3. The latter is about the density at which Hensel1 deduced that the electronic mean free path equalled the mean interatomic spacing, and which he took to be associated with the electronic-property related transition in the liquid phase.
Equation of state and thermodynamic properties of saturated and superheated mercury vapors up to 1650 K and 125 MPa
Experimental data on the compressibility, sound velocity, and saturation pressures have been generalized for mercury vapor at densities <3 g/cm2 based on the equation of state with the second, third, and fourth virial coefficients. The virial coefficients have been calculated using the three-parameter Lennard-Jones potential m-6. The data have been generalized using the nonlinear weighted least-squares method. The parameters of the models and their enlarged error matrix taking into account random and systematic (in the first approximation) errors of the experimental data have been determined. Tables of thermodynamic properties of the saturated and superheated vapor have been calculated. The enthalpy drop error has been correctly calculated on the isentropic curve of the superheated vapor taking into account covariations of the equation of state parameters.
Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules
The NICSzz-scan curves of aromatic organic, inorganic and “all-metal” molecules in conjunction with symmetry-based selection rules provide efficient diagnostic tools of the σ-, π- and/or double (σ + π)-aromaticity. The NICSzz-scan curves of σ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 A with the induced diatropic ring current arising from Tx,y-allowed transitions involving exclusively σ-type molecular orbitals. Broad NICSzz-scan curves (half-band width approximately higher than 3 A) characterize double (σ + π)-aromaticity, the chief contribution to the induced diatropic ring current arising from Tx,y-allowed transitions involving both σ- and π-type molecular orbitals. NICSzz-scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (σ + π)-aromatics where the π-diatropic ring current overwhelms the σ-type one. In the absence of any contribution from the σ-diatropic ring current, the NICSzz(0) value is close to zero and the molecule exhibits pure π-aromaticity.