Physical Sciences and Mathematics Commons^™

Structural Characterization Of Mixed Alkali Metal Bis(Trimethylsilyl)Amide Bases., Paul Williard, Michael Nichols

Michael A Nichols

No abstract provided.

Polymer Research In Austria. I: Introduction And The Facilities, Otto Vogl, Josef Schurz, Bernd Thrattnigg, Klaus Hummel, Wolfgang Daimler, Klaus Lederer

Otto Vogl

No abstract provided.

Japan-U.S. Seminar On Polymer Synthesis, Otto Vogl, Hiroyuki Nishide

Otto Vogl

No abstract provided.

Electrochemical And Spectroscopic Investigations Of The Properties Of Electrified Interfaces, Mark Anderson

Mark R. Anderson

No abstract is available at this time.

The Influence Of Cation Size Upon The Infrared Spectrum Of Carbon Monoxide Adsorbed On Platinum Electrodes, Mark Anderson, Jimin Huang

Mark R. Anderson

The infrared spectrum of carbon monoxide adsorbed on polycrystalline platinum electrodes in the presence of acetonitrile solutions is examined. Acetonitrile solutions provide a wide double layer region (approximately 4 V) in which to investigate the observed potential dependence of the infrared peak position. The wider window allows for better comparisons of experimental data with theoretical predictions than those which are available from measurements conducted in aqueous solutions. It is found that (i) near-monolayer surface coverage can be obtained from solutions saturated with CO, (ii) the coverage stays constant over roughly the entire double layer region, (iii) the CO adsorbs to …

Spectroelectrochemical Analysis Of Spontaneously Adsorbed Monolayers, Marilyn O'Grady, Mark Anderson

Mark R. Anderson

No abstract is currently available.

An Analytical Representation Of The Lowest Potential Energy Surface For The Reaction O(3 P)+Hcl (X  1Σ+)→Oh(X  2Π)+Cl(2 P), H. Koizumi, George C. Schatz, Mark S. Gordon

Mark S. Gordon

We present a new analytical representation of the lowest 3 A‘ energy surface for the reaction O(3 P)+HCl(X  1Σ+)→OH(X  2Π)+Cl(2 P). This surface is derived by fitting a b i n i t i o calculations, and adjustments are made to the barrier height so that rate constants derived from accurate quantum scattering calculations match the room temperature thermal rate constants. Contributions to thermal and state resolved rate constants arising from reaction on the lowest 3 A’surface are also considered. Comparisons of thermal and state resolved rate constants with experiment are good except at high temperature where the 3 A’ …

A Collaborative Summer Research Program For Community College Students, Chris Craney, Franklin Dehaan

Chris L. Craney

While the benefits of undergraduate research are well established, little attention has been paid toward involving community college students in such research. This paper describes a five-year-experience with a summer research program that includes Los Angeles area community college students working side-by-side with Occidental College students and faculty.

The Conformational Potential Energy Surface Of Glycine: A Theoretical Study, Jan H. Jensen, Mark S. Gordon

Mark S. Gordon

The conformational potential energy surface of nonionized glycine has been studied by using ab initio (6-310*, ST0-20) and semiempirical (AM1, PM3) methods. The MP2/6-31G*/ /RHF/6-310* potential energy surface was then used to calculate the Boltzmann equilibrium distribution and kinetics of conformational interconversion at various temperatures. The results of this study are compared to previous computational and experimental investigations of gas-phase glycine.

Structures And Bonding Of Group Iv Sulfur And Oxygen Propellane Derivatives, Kiet A. Nguyen, Marhsall T. Carroll, Mark S. Gordon

Mark S. Gordon

The RHF, ROHF, and GVB structures and energetics of group IV 2,4,5-trioxa[l.l.l]metallapropellanes, 2,4,5- trithia [ l.l.l]metallapropellanes, and their bicyclopentane analogues have been determined from ab initio molecular orbital theory by using both the 6-31G(d) basis set for all-electron calculations and the valence basis set with effective core potentials (ECP) developed by Stevens, Basch, and Krauss. Although they have extremely short bridgehead distances, these species possess fairly large natural orbital occupation numbers in the lowest unoccupied molecular orbitals, indicating significant diradical character. Structures and other properties determined by ECP calculations are in good agreement with the 6-31 G(d) all-electron calculations.

Spectroelectrochemical Analysis Of Metal Surfaces Modified With Thin Organic Films, Marilyn O'Grady, Mark Anderson

Mark R. Anderson

No abstract is currently available.

Determination Of The Vertical Ionization Potentials Of Small Sodium Clusters Using Path Integral Monte Carlo Calculations, Sean E. Hays, Randall W. Hall

Randall W. Hall

Predicted Enthalpies Of Formation For Methyl-Substituted Silaethylenes And Disilenes, Jerry A. Boatz, Mark S. Gordon

Mark S. Gordon

Enthalpies of formation of the methyl-substituted silaethylenes (CH3).H2_,Si=CH2 (n = 1, 2) and disilenes (CH3),.H~i=Si(CH3),H:~-m (n, m = Q-2) are predicted by using isodesmic reactions which relate the compound of interest to the parent silaethylene (H2Si=CH2) or disilene (H~i=SiH2), for which accurate enthalpies of formation have recently been determined. In turn, the enthalpies of formation of these methyl-substituted compounds are used in conjunction with homodesmic reactions to reevaluate the enthalpies of formation of the silicon-substituted cyclobutenes C.Si4-0H6 (n = Q-4).

Stabilization Of Β Positive Charge By Silicon, Germanium, Or Tin, Kiet A. Nguyen, Mark S. Gordon, Gen-Tai Wang, Joseph B. Lambert

Mark S. Gordon

Ab initio molecular orbital theory is used to study the β effect of carbon, silicon, germanium, or tin on the carbenium ions in H2R'MCH2CHR+ (R' = H; R = H, CH3). The relative stabilization energies of carbenium ions provided by M (M = C, Si, Ge, Sn) were determined by calculating the energy change in an isodesmic reaction using MP2/3-21G(d) (at SCF /3-21G* geometries) and MP2/6-31G(d) (at SCF /6- 31G(d) geometries) wave functions. The magnitude of the β effect is predicted to increase in the order C < Si < Ge < Sn. For R = H, the nonvertical cyclic structure is favored for the cations, whereas methyl substitution appears to stabilize the vertical acyclic arrangement.

Ab Initio Study Of Some Methylene And Silylene Insertion Reactions, David R. Gano, Mark S. Gordon, Jerry A. Boatz

Mark S. Gordon

The theoretical barriers and reaction energetics have been determined, using ab initio calculations at the MP4/6-3IG(d) level, with 3-2IG* geometries, for the insertions of methylene and silylene into the X-Y bonds of ethane, methylsilane, disilane, and cyclopropane and into the X-H bonds of disilane and ethane. A correlation was observed between barrier heights and lengths of substrate bonds. The largest barriers were observed for methylene and silylene inserting into the C-C bonds of ethane. The barriers became successively lower for the C-Si and Si-Si bonds. Steric interactions thus appear to be a major factor in determining barrier heights. The observed …

Nature Of The Si-N Bond In Silatranes, Mark S. Gordon, Marshall T. Carroll, Jan H. Jensen, Larry P. Davis, Larry W. Burggraf, R. Martin Guidry

Mark S. Gordon

Both ab initio and semiempirical calculations are used to investigate the structure and bonding in substituted silatranes. In agreement with gas-phase experiments, which fmd Si-N distances that are 0.25-0.35 A longer than those in the crystal phase, the Si-N distance (for example, in methylsilatrane) is predicted to be much larger than that observed in the crystal. Nonetheless, a bond critical point is found between Si and N, suggesting the existence of an Si-N bond in these compounds. It is found that the energy cost for constraining the Si-N distance in hydroxysilatrane to a value similar to that observed in the …

Chelation Of 2-Substituted 1-Lithoxides: Structural And Energetic Factors Of Relevance To Synthetic Organic Chemistry., Michael Nichols, Andrew Mcphail, Edward Arnett

Michael A Nichols

No abstract provided.

Characterization Of Adsorption By Electrochemical And Spectroscopic Methods, Mark Anderson

Mark R. Anderson

No abstract is available at this time.

Systematic Survey Of Cyclic Silicon-Oxygen Compounds, Michael W. Schmidt, Kiet A. Nguyen, Mark S. Gordon, John A. Montgomery Jr.

Mark S. Gordon

Compounds with 0, 1, 2, or 3 oxygen atoms bridging 2 silicon atoms are investigated by ab initio calculations. Two such series of compounds, with and without a formal central Si-Si bond, are considered. The triplet states of the former set are also examined. For some of these compounds, the present calculations represent the first time they have been examined at a sufficiently rigorous level of theory. For the compounds that are formally bonded, this level is two configuration SCF (TCSCF) for singlets and ROHF for triplet states, using split valence polarized basis sets. The main result is that no …

A Theoretical Study Of Some Reactions Of Hcsi-, Michael W. Schmidt, Mark S. Gordon

Mark S. Gordon

The ions HCSi- and H2CSiH- produced in recent flowing afterglow experiments are characterized structurally. Reactivity of the former ion with four molecules (C02, OCS, CS2, S02) is examined. Three of these species react in a sequence of intermediates of cyclic followed by acyclic structures, before reaching the final products.

Principal Resonance Contributors To High-Valent, Transition-Metal Alkylidene Complexes, Thomas R. Cundiari, Mark S. Gordon

Mark S. Gordon

The results of ab initio calculations are reported for prototypical high-valent, alkylidene complexes. Stationary points on each potential energy surface are characterized and compared to experimental information where available; as long as a suitably flexible valence basis set is used, good agreement between theoretically calculated and experimentally determined geometries is obtained. The complexes of interest include group IVB (Ti, Zr and Hf) and group VB (Nb and Ta) alkylidenes with hydride ligands as well as models for the four-coordinate, olefin metathesis catalysts (Mo-, W-, and Re-alkylidenes) which have been recently synthesized and characterized. In light of the fact that much …

The Influence Of Cation Size Upon The Infrared Spectrum Of Carbon Monoxide Adsorbed On Platinum Electrodes, Mark Anderson, Jimin Huang

Mark R. Anderson

No abstract is currently available.

The Influence Of Cation Size Upon The Infrared Spectrum Of Carbon Monoxide Adsorbed On Platinum Electrodes, Mark Anderson, Jimin Huang

Mark R. Anderson

No abstract is currently available.

A New Twist On Pseudorotation, Theresa L. Windus, Mark S. Gordon, Larry W. Burggraf, Larry P. Davis

Mark S. Gordon

For pentacoordinated structures in a trigonal bipyramidal ar· rangement, Berry1 proposed a "pseudorotation" mechanism whereby two such isomers can interconvert through a tetragonal transition state (TS). This Berry pseudorotation mechanism was demonstrated explicitly for SiH5- by following the MP22/6· 31G(d)3 minimum energy path4 (MEP).

Sniftirs Study Of The Behavior Of The Spectrum Of Carbon Monoxide Adsorbed On A Platinum Electrode In Alcoholic Solvents, Andrea Russell, Daniel Blackwood, Mark Anderson, Stanley Pons

Mark R. Anderson

The vibrational spectrum of carbon monoxide as a function of coverage in various alcoholic solvents was investigated using the SNIFTIRS technique. At low coverage the potential dependence of the band position was found to be linearly dependent on the inverse of the bulk dielectric constant of the solvent. An electrostatic model was developed to represent the interaction between adjacent adsorbate molecules. This model provides evidence in support of an island formation mechanism.

Gas-Phase Chemistry Of The Dimethylaluminum Oxide Ion And Related Aluminum Oxide Ions: Comparison Of Reactivity With Siloxide Ions, Robert Damrauer, Michèle Krempp, Michael W. Schmidt, Mark S. Gordon

Mark S. Gordon

The anion [(CH3hAIOt (1) has been prepared in a flowing afterglow selected ion flow tube (FA-SIFT) by ion selection from the reaction mixture of trimethylaluminum dimer and hydroxide. This unusual ion is quite reactive and has been extensively studied. It reacts with halogen-containing compounds of several types, including fluorobenzene, chlorobenzene, bromofluorobenzene, acetyl chloride, and HF, to give [(CH3hAI(OH)Xt, where X = F, Cl, and Br. Its chemistry with hexafluorobenzene and silicon tetrafluoride has also been detailed as have a number of reactions with carboxylic acids, esters, anhydrides, sulfur-containing neutrals, alcohols, water, and ammonia. The dominant reaction pattern of 1 involves …

The Interaction Between Dislocations And Intergranular Cracks, H. Zhang, Alexander H. King, R. Thomson

Alexander H. King

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in …

Effect Of Hydration And Dimerization Of The Formamidine Rearrangement, Kiet A. Nguyen, Mark S. Gordon, Donald G. Truhlar

Mark S. Gordon

Ab initio molecular orbital theory is used to predict the geometry of the transition state and the energy barrier for the double-proton transfer in formamidine dimer, using SCF /6-31 G(d,p) and MP2/6-31 G(d,p) wave functions, respectively. Intramolecular hydrogen transfer in the uncomplexed monomer (I) and double-proton transfer in the mixed dimer of formamidine and water (2) are also investigated at several levels of theory. All computational levels predict the barrier for the uncomplexed reaction (I) to be approximately twicdhat for the hydrated reaction (2). Isomerization by double-proton transfer in the dimer (3) is predicted to be the most favorable process. …

Characterization Of Sh Groups In Porin Of Bovine Heart Mitochondria. Porin Cysteines Are Localized In The Channel Walls., Philadelphia University

Philadelphia University, Jordan

No abstract provided.

Ab Initio Study Of The Intermolecular Potential Of Ar–H2o, G. Chalasinski, M. M. Szczesniak, Steve Scheiner

Steve Scheiner

The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential‐energy surface of Ar–H₂O. The surface is very isotropic with the lowest barrier for rotation of ∼35 cm⁻¹ above the absolute minimum. The lower bound for D_e is found to be 108 cm⁻¹ and the complex reveals a very floppy structure, with Ar moving freely from the H‐bridged structure to the coplanar and almost perpendicular arrangement of the C₂ –water axis and the Ar–O axis, ‘‘T‐shaped’’ structure. This motion is almost isoenergetic (energy change …