Article

Density functional theory is used to characterize the lowest energy excited spin triplet orbital configurations of square-planar halide complexes of palladium(II). Calculations for the eg –> b1g orbital excitation (D4h labels) predict a non-totally symmetric distortion along the b1g normal coordinate, leading to unequal bond lengths for perpendicular metal-ligand bonds (D2h symmetry). Calculated bond length changes are 0.15 Å (0.11 Å) and 0.05 Å (0.00 Å) for PdCl42- (PdBr42-). These values compare favorably to the emitting-state distortions of 0.12 Å and 0.09 Å for K2PdCl4 (0.12 Å, and 0.07 Å for K2PdBr4) determined from resolved single-crystal luminescence spectra. The calculations indicate that the non-totally symmetric distortion is an intrinsic molecular property of these complexes.Key words: palladium(II) complexes, excited state distortions, density functional theory.

InP under high pressures

The direct energy gaps, Eg, and the indirect gaps at the X point, E(X), of GaAs and AlxGa1−xAs alloys are essentially linear functions of hydrostatic pressure, P. Recent photoluminescence measurements of Tozer et al. for InP under high pressures, however, found that Eg(P) is not quite linear, but bends down slightly at high pressures. Using the first-principles pseudofunction method, we have calculated Eg and E(X) as functions of pressure, as well as the zero-temperature equation of state P(V). Our calculated gap curve for InP, Eg(P), bends down slightly, as found in photoluminescence studies. The slope dEg/dP is 8.8 meV/kbar for small pressures P, and is in good agreement with the experimental value, 8.32 meV/kbar. The observed nonlinearity in the dependence of Eg on pressure for InP is attributed to a large derivative of the bulk modulus with respect to pressure. The calculated bond length, bulk modulus, and critical pressure for a phase transition from the zinc blende to a rocksalt structure, and the unit cell volume change at this phase transition are all in good agreement with the data.

The molecular structure of ammonia oxide (NH3O). An ab initio study

Ab initio molecular orbital theory is used to determine the molecular structure of ammonia oxide (NH3O). It is found that the N-O bond length is considerably overestimated by minimal (STO-3G), split-valence (4-31G and 6-31G) and large sp basis sets. This fault is rectified when polarization functions on nitrogen and oxygen are included in the basis (6-31G*) leading to the best theoretical value for the N-O length of 1.377 A. Electron correlation has little effect on the calculated bond length. Calculations (STO-3G and 4-31G) are also reported for trimethylamine oxide.