Christian Thierfelder

A highly accurate potential energy curve for the mercury dimer.

The potential energy curve of the electronic ground state of the mercury dimer based on CCSD(T) calculations at the complete basis set (CBS) limit, including corrections for the full triples DeltaT and explicit spin-orbit (SO) interactions at the CCSD(T) level of theory, is presented. In the far long-range part, the potential energy curve is complemented by symmetry-adapted perturbation theory calculations. Potential curves of an analytically simple, extended Lennard-Jones form are obtained from very accurate fits to the CBS/CCSD(T)+SO and CBS/CCSD(T)+SO+DeltaT data. The Hg(2) potential curves yield dissociation energies of D(e)=424/392 cm(-1) and equilibrium distances of r(e)=3.650/3.679 A at the CBS/CCSD(T)+SO and CBS/CCSD(T)+SO+DeltaT levels of theory, respectively. By including perturbative quadruple corrections in our coupled-cluster calculations and corrections from correlating the 4f-core, we arrive at a final dissociation energy of D(e)=405 cm(-1), in excellent agreement with the experimentally estimated value of 407 cm(-1) by Greif and Hensel. In addition, the rotational and vibrational spectroscopic constants as well as the second virial coefficient B(T) in dependence of the temperature T are calculated and validated against available experimental and theoretical data.

Kinetic and Thermodynamic Stability of the Group 13 Trihydrides

The kinetic and thermodynamic stabilities of the group 13 hydrides EH(3) (E = B, Al, Ga, In, Tl, E113) are investigated by relativistic density functional and wave function based theories. The unimolecular decomposition of EH(3) --> EH + H(2) becomes energetically more favorable going down the Group 13 elements, with the H(2)-abstraction of InH(3), TlH(3), and (E113)H(3) (E113: element with nuclear charge 113) being exothermic. In accordance with the Hammond-Leffler postulate, the activation barrier for the dissociation process decreases accordingly going down the group 13 elements in the periodic table shifting to an early transition state, with activation energies ranging from 88.4 kcal/mol for BH(3) to 41.3 kcal/mol for TlH(3) and only 21.6 kcal/mol for (E113)H(3) at the scalar relativistic coupled cluster level of theory. For both TlH(3) and (E113)H(3) we investigated spin-orbit effects using Dirac-Hartree-Fock and second-order Møller-Plesset theory to account for electron correlation. For (E113)H, spin-orbit coupling results in a chemically inert closed 7p(1/2)-shell, thus reducing the stability of the higher oxidation state even further. We also investigated the known organothallium compound Tl(CH(3))(3), which is thermodynamically unstable similar to TlH(3), but kinetically very stable with an activation barrier of 57.1 kcal/mol.

, Nuclear quadrupole moment of 139La from relativistic electronic structure calculations of the electric field gradients in LaF, LaCl, LaBr and LaI

Relativistic coupled cluster theory is used to determine accurate electric field gradients in order to provide a theoretical value for the nuclear quadrupole moment of (139)La. Here we used the diatomic lanthanum monohalides LaF, LaCl, LaBr, and LaI as accurate nuclear quadrupole coupling constants are available from rotational spectroscopy by Rubinoff et al. [J. Mol. Spectrosc. 218, 169 (2003)]. The resulting nuclear quadrupole moment for (139)La (0.200+/-0.006 barn) is in excellent agreement with earlier work using atomic hyperfine spectroscopy [0.20(1) barn].