Search results for "geometry."

On the geometry of the HO3 radical

2008

Abstract We discuss the equilibrium structure of the hydrogen trioxy radical (HO3). The CCSD(T) geometry at the approximate basis set limit, in conjunction with the geometry obtained using the CCSDT method and a moderate basis set, suggests an equilibrium HO–OO bond length of approximately 1.59 A.

GERMANIUM DICARBIDE: EVIDENCE FOR A T−SHAPED GROUND STATE STRUCTURE

2017

The equilibrium structure of germanium dicarbide GeC2 has been an open question since the late 1950s. Although most high-level quantum calculations predict an L-shaped geometry, a T-shaped or even a linear geometry cannot be ruled out because of the very flat potential energy surface. By recording the rotational spectrum of this dicarbide using sensitive microwave and millimeter techniques, we unambiguously establish that GeC2 adopts a vibrationally averaged T-shaped structure in its ground state. From analysis of 14 isotopologues, a precise r0 structure has been derived, yielding a Ge–C bond length of 1.952(1) A and an apex angle of 38.7(2)°.

An ab initio study of the tautomeric equilibria of the N-oxides of hydroxypyridines in the vapour phase

1993

Abstract An ab initio self-consistent field molecular orbital study of the N-oxides of hydroxypyridines has been carried out. The optimized structures have been obtained at the 6-31G ∗ level, and the energy values have been computed at the 6-31G ∗ and MP2-6-31G ∗ //6-31G ∗ levels. The tautomerization energies for the three couples of systems in the vapour phase have been evaluated.

Continuum Monte Carlo simulation of phase transitions in rod-like molecules at surfaces

1994

Stiff rod-like chain molecules with harmonic bond length potentials and trigonometric bond angle potentials are used to model Langmuir monolayers at high densities. One end of the rod-like molecules is strongly bound to a flat two-dimensional substrate which represents the air-water interface. A ground-state analysis is performed which suggests phase transitions between phases with and without collective uniform tilt. Large-scale off-lattice Monte Carlo simulations over a wide temperature range show in addition to the tilting transition the presence of a strongly constrained melting transition at high temperatures. The latter transition appears to be related to two-dimensional melting of th…

A theoretical determination of the dissociation energy of the nitric oxide dimer

1994

Multi-reference CI methods have been applied to determine the dissociation energy and structure of thecis-N2O2 molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional…

Experimental and theoretical studies of the molecular and crystal structures of trialkoxy- and chlorodialkoxy-stibanes

2001

The molecular structures of triisopropoxystibane, Sb((OPr)-Pr-i)(3), and chlorodiisopropoxystibane, SbCl((OPr)-Pr-i)(2), were determined in the solid state by single crystal X-ray diffraction. Sb((OPr)-Pr-i)(3) forms discrete centrosymmetric dimers in the solid state via Sb . . .O-Sb interactions, leading to pseudo trigonal bipyramidal configurations of the four co-ordinate Sb atoms, while SbCl((OPr)-Pr-i)(2) forms chains via Sb . . .O-Sb and Sb . . . Cl-Sb bridges, resulting in five-co-ordinate Sb atoms with pseudo octahedral configurations. Comparison of the solid state structures and the density functional optimized molecular structures of Sb(OMe)(3), SbCl(OMe)(2) and their dimers reveal…

Influence of Structural Isomerism on the Electronic Properties of Extended Phthalocyanines

1993

Abstract The electronic structure of isomeric naphthalocyanines (H2Nc) is investigated using the nonempirical valence effective Hamiltonian (VEH) technique. The way the outer benzene rings are annelated (linearly as in 2,3-H2Nc or angularly as in 1,2-H2Nc) is shown to determine very important changes in the electronic properties. While similar properties to those of phthalocyanine are calculated for 1,2-H2Nc, lower oxidation potentials and red-shifted optical absorptions are predicted for 2,3-H2Nc in agreement with experimental data. The isomerism resulting from the different relative positions of the angularly annelated benzene rings in 1,2-H2Nc is shown to have almost no effect on the ele…

Anthropogenic disturbance and diversity of species: polypores and polypore-associated beetles in forest, forest edge and clear-cut

2005

In boreal coniferous forests, artificial edges often modify the habitat, increasing the likelihood that the diversity and composition of species changes. This study examined the assemblage of polypores and polypore-associated beetles at the edge of mature managed spruce-dominated forests and clear-cuts. The highest number of polypore occurrences and the greatest diversity of polypore species occurred at the clear-cut. In south-facing edges polypores occurred closer to the edge both in clear-cut and in forest than in the north-facing edges. The number of polypore-associated beetle individuals was greatest in the clear-cut, but there was no effect of edge on species richness of beetles. Orien…

Boundary angles, cusps and conformal mappings

1986

Let f be a conformal mapping of a bounded Jordan domain D in the complex plane onto the unit disk . This paper examines the consequences for the local geometry of D near a boundary point z 0 of the mapping f-or, to be more precise, of the homeomorphic extension of this mapping to the closure of D—satisfying a Holder condition at z 0 or, alternatively, of its inverse satisfying a Holder condition at the point f(z 0). In particular, the compatibility of Holder conditions with the presence of cusps in the boundary of D is investigated.

Bounded Geometry, Growth and Topology

2011