Orbital Contour Research Articles

Ab initio study of CO and H 2 interaction on ZnO surfaces using a small cluster model

We have studied the adsorption of H 2 and CO molecules, as well as the dissociation of H 2, on the (ZnO) 6 cluster model using the ab initio Hartree-Fock method. The effective core potential was used for Zn, C, and O atoms at double-zeta-type valence basis set level, whereas for H we used Dunning's basis set. We have also added polarization and diffuse functions to the O, C, and H basis set. The CO molecule interacts with the lowest coordination zinc sites which are located on the edge between the (0001) and (101̄0) surfaces. The decrease in CO bond length upon adsorption on ZnO surfaces is associated with the charge transfer from CO to the surface. Our calculations indicate the 5σ orbital from adsorbed CO stabilized to a 1.56 eV deeper energy. Of all the configurations investigated, the molecular H 2 interaction has the lowest binding energy with a decrease in H 2 bond strength. The H 2 molecule also dissociates on the zinc and oxygen sites of the ZnO cluster, and the preferential dissociation site is the oxygen which has a coordination number of two. The H 2 dissociation shows a large stabilization energy for the most stable adsorption site which is the lowest coordination site. Molecular CO and H 2 adsorption yields a smaller change in the estimated energy gaps and ionization potentials. We have also analysed the geometry of the adsorbed molecules, the Mulliken charge, the orbital SCF energies, and also the molecular orbital densities and contour plots. Our results are compared with the available experimental data.

Theoretical Study on the Interaction Between Dopamine and its Receptor byab initioMolecular Orbital Calculation

Dopamine has been implicated in the function of a diverse set of central nervous system and peripheral functions. We theoretically evaluated the chemistry of interaction between dopamine and its receptor usingab initiomolecular orbital calculation. First, we calculated the total energy of dopamine on either a protonated or deprotonated molecule at the meta- or para-position hydroxy group of the catechol ring, and then evaluated the hydrogen bond effect in these hydroxy groups. These results suggested that the meta-position hydroxy group was liable to be protonated, and subsequently deprotonated by a negatively charged receptor site. It was considered that proton flopping, which occurred within the receptor siteviathe meta-position hydroxy group, appeared to be essential for exerting the biological action of dopamine. On the other hand, the para-position hydroxy group of the catechol ring contributed to stabilization of a dopamine molecule at the receptor site through a hydrogen bond. Second, we showed that the side-chain amino group of dopamine was readily protonated and bound a negatively charged receptor site by coulomb interaction. Third, we calculated the highest occupied molecular orbital and lowest unoccupied molecular orbital to elucidate chemical reactivities of these functional groups on the electron level. From the molecular orbital contour maps, it was suggested that frontier orbital interaction was involved in the dopamine–receptor interaction, in which the meta- and para-position hydroxy groups may function as a proton acceptor and a proton donor, respectively. Considering these theoretical results together, we hereby propose a model of the dopamine–receptor interaction: (1) a protonation–deprotonation at the meta-position hydroxy group takes place, (2) the protonated side-chain amino group of dopamine binds to a negatively charged receptor site by an ionic bond, and (3) the para-position hydroxy group not only contributes to stabilization for dopamine binding but may also enhance the protonation–deprotonation at the meta-position through bond interaction along the π-bond between OH and the benzene ring.

Structure, properties and quantum chemistry studies on non-stoichiometric compounds of (Nb yTi 1 − y)C x

Non-stoichiometric compounds of (Nb y Ti 1 − y )C x , in which the amount of Nb element added is increased from zero to 40% (weight percent), synthesized with self-propagating high temperature synthesis, are studied with SCF-X α-DV, a quantum chemistry calculating method. The chemical bonding is studied to discuss the relation between structures and properties. Several classes of models in which there is no vacancy, one vacancy or two vacancies have been calculated. From the calculated results of bond order, a measure of covalent bond strength, and molecule orbital contour map, an audio-visual method to discuss chemical bonding, we conclude that when Nb element added increases, the vacancies increase correspondingly, the covalent component of the chemical bonds of the samples decreases while the metal-bonding component increases, so the hardness and electrical resistance of the samples decrease.

Electronic structure of exohedral interactions between C 60 and transition metals

The electron distribution and orbital interactions of C 60 with metals coordinated at different sites on the outside of the fullerene are evaluated. These sites include the position of a metal atom directly above a carbon atom (η 1 site), the metal atom centered above two carbons of a pentagon or above two carbons between two pentagons (both η 2 sites), the metal atom centered above a pentagon (η 5 site), and the metal atom centered above a hexagon (η 6 site). The frontier orbitals of C 60 are illustrated first with three-dimensional orbital contour plots. A palladium atom is then used to probe the bonding at the different sites on the C 60 surface. The results with Pd 0 are compared to our earlier study with the harder Ag + ion in order to examine the effects of metal electron richness and size. In addition, these results are compared with the bonding to more traditional ligands that represent the hapticity of these sites, such as methyl (η 1), ethylene (η 2), cyclopentadienyl (η 5), and benzene (η 6). The strength of the metal-C 60 interaction and the amount of charge delocalized from the metal to C 60 is sensitive to the site of coordination, the electron richness of the metal, and distortions in the geometry of C 60. As discussed in our previous work, the frontier orbitals of C 60 are well-suited for synergistic bonding of a metal atom to a carbon-carbon pair in an alkene-like fashion, in which the HOMO of C 60 donates carbon-carbon π bonding electron density to the metal, and the LUMO of C 60 accepts electron density from the metal into a carbon-carbon π* antibonding orbital. Although the HOMO and LUMO of C 60 describe the basic interaction, many frontier orbitals are involved. The site above the CC bond between two pentagons is favored over the site above the CC bond within a pentagon, and the interaction above the other sites is indicated to be net repulsive by these calculations. The differentiation between these sites increases with the electron richness of the metal center. The bonding of the metal to C 60 is generally weaker than to the small ligands, except for very electron rich metal centers where the bonding to the η 2 site between pentagons apparently becomes stronger than the bonding to ethylene.

Structure of Os(CO)4(C2H4), an osmacyclopropane

{sup 13}C-{sup 13}C for an ethylene coordinated to Os(CO){sub 4} has been determined as 39.0 (2) Hz from the {sup 1}H NMR spectrum of Os(CO){sub 4}({eta}{sup 2}-{sup 13}C{sub 2}H{sub 4}). The molecular structure of Os(CO){sub 4}({eta}{sup 2}-C{sub 2}H{sub 4}) (1) has been determined by single-crystal X-ray diffraction. The geometry of 1 is approximately trigonal bipyramidal, with the ethylene carbons twisted out of the equatorial plane by 4.0{degrees}. The axial carbonyls of 1 tilt toward the coordinated ethylene, with a C1-Os-C1` angle of 171.3 (5){degrees}. The optimal geometries of Os(CO){sub 4}, H{sub 2}Os(CO){sub 4}, and 1 have been calculated by Hartree-Fock methods. The orbital amplitude contour diagrams of a GVB(6/12) wave function for 1 show that the axial bending occurs in order to mix in virtual p{sub {pi}} character and improve back-bonding to the equatorial carbonyls; they also show that 1 is best described as a metallacyclopropane. 57 refs., 6 figs., 6 tabs.

Orbital reorganization and its energies in the interaction of CO with Sc, Fe, and Cu

The interaction of CO with transition metals (M = Cu, Fe, and Sc) is analyzed using a newly developed method within the framework of the Hartree–Fock approximation. This method reveals reorganization of each orbital by the interaction and its energy contribution. To avoid the basis-set dependence in the energy partitioning, the orbital reorganization energy includes both polarization and charge-transfer effects; however, these effects are clearly distinguished by using orbital contours. The interaction in M–CO is discussed not only in terms of widely accepted components, such as metal 4s–4pσ polarization, CO 5σ – metal 3dσ donation, and metal 3dπ – CO 2π* backdonation, but also by using newly found components, metal 3dσ – 4s and 4s–3dσ polarization, CO 5σ – metal 4pσ donation, metal 3dσ – CO 6σ* back-donation, and CO 1π – 2π* polarization. Keywords: metal carbonyl, interaction energy, orbital reorganization.

Use of irradiated bovine cartilage in orbital reconstructive surgery: A five-year experience

After a brief consideration on the use of biological and synthetic materials in orbital reconstructive surgery, the authors report their experience with implants of irradiated bovine cartilage. This material has been used in 50 patients suffering from orbital fractures with or without enophthalmos, orbital tumors and endocrine proptosis for reconstruction of the orbital floor and of the orbital contour. In a follow-up ranging from four months to five years these implants were well tolerated, they were easily shaped and implantable, and not subject to any significant resorption.

Structure and reactivity of PMMA ion radicals—an ab-initio approach

Ab initio molecular orbital (MO) calculations were carried out on the anion radical of methyl isobutyrate, a model of the poly(methylmethacrylate) (PMMA) anion. Calculations were also made on the cation radical for comparison. The results indicated that a strong absorption band at <320 nm and a weak one at 440 nm were attributed to the π-π ∗ and n-π ∗ transitions of the PMMA anion, respectively. It was found, from the geometry optimization, that the carbonyl group of the anion was bent and the carbonyl oxygen had deviated from the sp 2 plane of the carbonyl carbon. Molecular orbital contour maps of singly occupied MO suggested that the excess electrons were mainly distributed on the carbonyl group of the polymer. The stability of the PMMA anion and cation is discussed in terms of the potential energy curves calculated as a function of the O-CH 3 distance.

Floating C-shaped orbital osteotomy for orbital rim advancement in craniosynostosis: preliminary report

A method of lateral orbital rim advancement is described for periorbital deformities associated with coronal and metopic synostosis in infants. The technique offers the advantages of a smooth lateral rim contour and improvement in accompanying malar recession. In 13 patients with follow-up periods of up to 2 years following surgery, improved orbital contour has been appreciated. Further observation is warranted to determine whether this improvement will last into adulthood.

Draw 2D, draw 3D: MOPAC 2- and 3-dimensional graphical output written using the PHIGS graphics standard

Programs, written in graPHIGS, to display 2- and 3-dimensional contour plots of orbital density of molecular orbitals are described and included on disk. The 3D image is created by “stack plotting” 2-dimensional slices of the molecular orbital density. Features including zoom, xyz-rotation, writing pixel images to a file and superposition of stick plots of the molecule on the orbital contours.

Effects of In-Plane π’ Bonding on Electronic Transition Energies for Inorganic Polymers

ABSTRACTThe electronic structure of organic and inorganic polymeric systems are well described in terms of their molecular symmetry, even with the large bond polarity shown by such systems as polyphosphazenes. We have performed calculations using the semi-empirical CNDO/1 method to determine the valence electronic structure for a series of model phosphonitrilic and organic compounds. The optical transition energies for phosphonitrilic compounds are greater than their organic counterparts as a result of in-plane π’ bonding interactions. The extent of these interactions is modulated by the electronegativity of the substituent groups on the phosphorus atoms. We report values for the vertical ionization energy and electronic absorption wavelengths, and use molecular orbital contour analysis to show the effects of ligand electronegativity on the π’ network.

Inverted anatomic tracing: A guide to establishing orbital tissue contours for the oculofacial prosthesis

A technique is described to aid the maxillofacial prosthetic technician in contouring an oculofacial prosthesis. This technique should reduce clinical time and improve prosthesis results.

Thermolysis of trimethylsilyl esters: an ultraviolet photoelectron spectroscopy study

The thermolytic behaviour of trimethylsilyl trifluoromethanesulfonate, 1, trimethylsilyl trifluoroacetate, 2, and trimethylsilyl acetate, 3, has been investigated by ultraviolet photoelectron spectroscopy. Acetate 3 undergoes decomposition only to a small extent at 800 °C via the mechanism shown in Scheme 1 (X = Si); only acetic acid and starting material are detected. In contrast[Formula: see text]with this result, 1 and 2 decompose completely at 725–800 °C and yield products which cannot be derived via the mechanism shown in Scheme 1. Evidence is presented to support our proposal that the thermolysis of 1 yields trimethylsilyl fluoride, 6, and difluorooxathirane dioxide, 7, as primary products. The photoelectron spectra of 1, 2, 3, 6 and trimethylsilanol, 9, are presented. Molecular orbital eigenvalues of dimethylsilene, 4, dimethylsilanone, 5 (calculated using AMPAC and Gaussian 82), 6 and 9 (AMPAC) are reported. Molecular orbital contour diagrams are given for selected MOs of 6 and 9.

Electronic structure of the phosphonitrilic trimer?role ofd orbitals in chemical bonding

Ab initio molecular orbital calculations were performed on a series of phosphazene trimer molecules to elucidate the electronic structure of these systems. The role of the d orbitals was analyzed from comparison of the molecular orbital contour calculations performed both with and without d orbitals in a split valence basis set description. The results indicate that, although the major geometric aspects of these systems can be described without invoking the use of d orbitals, these orbitals are essential to properly describe the electronic structure. The d orbital involvement in out-of-plane π bonding contains elements of both the classical Craig, Paddock, and Mitchell [1–3] and Dewar et al. [4] bonding schemes; the d orbital effects on in-plane bonding modes are also substantial. The charge distribution in these systems is best described as a zwitterionic form, because a significant amount of charge accumulates on the ring nitrogens.

Experimental investigation of the valence orbital momentum distributions and ionization energies of the noble gases by binary (e, 2e) spectroscopy

A binary (e. 2e) spectrometer has been modified to obtain significantly improved momentum resolution ▪. Using this apparatus a systematic study of the ionization of all the valence orbitals of the noble gases: He, Ne, Ar, Kr and Xe has been carried out at an impact energy of 1200 eV plus the binding energy. Binding-energy spectra have been obtained at a series of azimuthal angles (corresponding to different electron momenta) for each target gas. In Ar, Kr and Xe the pole strength for ns ionization is severely split among several final ion states and the intensities are compared with earlier results from (e, 2e) spectroscopy. X-ray photoelectron spectroscopy and theoretical calculations. The ns and np atomic orbital (AO) electron-momentum distributions have been measured for the noble gases and the results, which give directly the squares of the AO momentum-spade wavefunctions, are compared with the square of Fourier transformed position-space wavefunctions of Hartree-Fock (HF), double-zeta (DZ) and single-zeta (SZ) quality. Excellent agreement is obtained between the experiment and Hartree-Fock calculations. Atomic orbital momentum density and position density contour maps have also been generated using Hartree-Fock wavefunctions. The maps have been used to provide a complementary discussion of position-and momentum-space properties of the noble-gas group of elements in the periodic table. Trends are discussed in the momentum distributions, density maps in position and momentum space and also the binding-energy spectra with reference to the electronic structure of the noble gases.

Traumatic Enophthalmos

Traumatic enophthalmos, either following orbital floor fracture or enucleation, is caused by decreased orbital volume.Volume replacement, both surgical and/or nonsurgical, provides a direct treatment.Surgical treatment can increase orbital volume by reducing the herniated orbital tissue and/or implanting alloplastic or autogenous material.When a seeing eye is present, implant surgery may compromise vision; volume replacement must be judicious.Alternative surgical management creates the illusion that little or no enophthalmos exists by enlarging the palpebral fissure or changing orbital contour.

Effects of bridging hydrogens on metal-metal bonds. 2. UV photoelectron and UV-visible spectra and quantum chemical calculations for Fe3(.mu.-H)3(CO)9(.mu.3-CMe) and Co3(CO)9(.mu.3-CMe)

The valence-level photoelectron spectrum of Fe/sub 3/(..mu..-H)/sub 3/(CO)/sub 9/(..mu../sub 3/-CCH/sub 3/) (II) has been measured in the gas phase with He I and Ne I radiation, and the UV-visible spectrum has been measured in solution. The observed bands in the former are assigned on the basis of model compound spectra, intensity changes with photon energy, and relative band areas. Comparison of the results with similar measurements on isoelectronic Co/sub 3/(CO)(..mu../sub 3/-CCH/sub 3/) (I) reveals significant differences associated with the presence of the bridging H atoms in II. These are described in terms of protonation of the M-M bonds in going from I to II. Molecular orbital calculations of the Fenske-Hall type on I and II corroborate both the assignment of the spectra and the differences in going from I to II. Examination of the results of Mulliken population analyses and selected orbital contour diagrams clearly demonstrates the essential localized, hydridic, and ligandlike behavior of the bridging H atoms in II. The calculations on I and II also demonstrate that the cluster bonding of Co(CO)/sub 3/ and Fe(CO)/sub 3/ fragments in these molecules is adequately represented by CH and BH fragments. 8 figures, 3 tables.

ChemInform Abstract: A THEORETICAL POTENTIAL ENERGY SURFACE STUDY OF SEVERAL STATES OF THE METHOXY RADICAL

Several low‐lying potential energy surfaces of the methoxy radical have been studied at C3v conformations using ab initio quantum chemical techniques. A double‐zeta quality basis set augmented with polarization and diffuse functions has been used throughout. Eight doublet and quartet states have been characterized as a function of C–O distance. The equilibrium conformation of the 2E ground state is found (RCO = 1.405 A, RCH = 1.112 A, ϑHCO = 111.3°), and the harmonic vibrational frequencies of the three a1 modes are calculated (3118, 1330, and 1017 cm−1). The ? 2A1←? 2E vertical excitation energy has been estimated to be 4.01 eV. The wave functions for the ? and ? states have been analyzed in terms of their dipole moments, population analyses, and orbital contour plots.

A theoretical potential energy surface study of several states of the methoxy radical

Several low-lying potential energy surfaces of the methoxy radical have been studied at C3v conformations using ab initio quantum chemical techniques. A double-zeta quality basis set augmented with polarization and diffuse functions has been used throughout. Eight doublet and quartet states have been characterized as a function of C–O distance. The equilibrium conformation of the 2E ground state is found (RCO = 1.405 Å, RCH = 1.112 Å, ϑHCO = 111.3°), and the harmonic vibrational frequencies of the three a1 modes are calculated (3118, 1330, and 1017 cm−1). The ? 2A1←? 2E vertical excitation energy has been estimated to be 4.01 eV. The wave functions for the ? and ? states have been analyzed in terms of their dipole moments, population analyses, and orbital contour plots.

On the validity of the isolobal principle: Pentaborane(9) and its ferraborane derivatives

We have completed Fenske-Hall LCAO-MO-SCF calculations on B 5 H 9 , 1-Fe(CO) 3 B 4 H 8 , 2-Fe(CO) 3 B 4 H 8 , and 1,2-[Fe(CO) 3 ] 2 B 3 H 7 . Comparison of orbital contour diagrams of the a 1 and e cluster MO's for B 5 H 9 and 1-Fe(CO) 3 B 4 H 8 demonstrates the validity of the isolobal principle. In addition it is found that the apical and basal BH units of B 5 H 9 have practically identical Mulliken overlap populations for framework cluster-type interactions. Further, in all the ferraboranes the 1-Fe(CO) 3 (apical) units have a larger cluster-type Mulliken overlap population than do the 2-Fe(CO) 3 (basal) units. The Fe(CO) 3 units have less electronic charge than do the BH units. The cluster-type Mulliken overlap population for an Fe(CO) 3 group is much less than that of the isolobal BH unit, but this may result from an artifact of the Mulliken overlap population analysis.