Physical Sciences and Mathematics Commons^™

Theoretical Studtes Of The Insertion Reactions Of Atomic Carbon And Silicon Into Methane And Silane, Shogo Sakai, John Deisz, Mark S. Gordon

Mark S. Gordon

The mechanisms for the insertions of atomic (ID and 3P) carbon and silicon into the C-Hand Si-H bonds of methane and silane are investigated by ab initio SCF methods, many body perturbation theory, and a localized molecular orbital (LMO) analysis. The LMO analysis shows that the insertion of 1D atoms into CH4 and SiH4 may be classified into two types: cationic hydrogen transfer and anionic hydrogen transfer. For the triplet atoms the LMO analysis suggests two different insertion reaction mechanisms: the near abstraction and the pull-push mechanisms.

Effects Of Pollution On Critical Population Dynamics, R. Kree, B. Schaub, Beate Schmittmann

Beate Schmittmann

We investigate the effects of pollution on a population that is on the brink of extinction. In the vicinity of the associated critical point, the temporal scales of the population density fluctuations are found to be completely governed by the diffusive behavior of the pollution density fluctuations. Moreover, the mean value of the population density is found to vanish with a larger power-law exponent in the presence of pollution density fluctuations. Results are obtained within a renormaliza- tion-group calculation to O(ε) (ε=4-d, d being the spatial dimension).

Mechanistic Studies Of The Far-Uv Photochemical Ring-Opening And Cleavage Reactions Of 1, 1-Dimethyl-1-Silacyclobut-2-Ene, Mark G. Steinmetz, B. S. Udayakumar, Mark S. Gordon

Mark S. Gordon

Direct photolyses of 1,1-dimethyl-1-silacyclobut-2-ene (1) at 214 nm in tert-butyl alcohol gave 29% tert-butoxydimethyl(2-propenyl)silane (2), 4.3% (Z)-tert-butoxydimethyl(1-propenyl)silane [(Z)-3], 6.9% (E)-tert-butoxydimethyl(1-propenyl)silane [(E)-3], and 5.9% tert-butoxytrimethylsilane (4) at 49% conversion. Products 2-4 were primary, and the total quantum yield of formation was 0.11. Use of tert-butyl alcohol-0-d led to >98% monodeuteration: 2-dl had 93.5% of the label at cl and 6.5% at c3 of the 2-propenyl group, (E)- and (Z)-3-d1 [(E),(Z)-3-dd were labeled >95% at C3 of the 1-propenyl group, and 4-d1 was deuterated at a silyl methyl. Cleavage of a silacyclopropylmethylene intermediate to 1,1-dimethyl-1-silaethene accounts for the labeling of 4-d1 and …

Heats Of Formation Of Alkylsilanes, Mark S. Gordon, Jerry A. Boatz, Robin Walsh

Mark S. Gordon

Theoretical heats of formation at 298 K for several alkylsilanes, predicted at the MP2/6-31G(d) level of theory, are compared with recently obtained experimental and additivity values. Excellent agreement is obtained between the ab initio and additivity values and with the more reliable experimental values for acyclic alkylsilanes. The ab initio heats of formation for the silacycloalkanes permit the evaluation of strain energy increments for the additivity scheme. Comparison is made with limited experimental data.

Precipitation Fluctuations Over Global Land Areas Since The Late 1800'S, Henry F. Diaz, Raymond S. Bradley, J. K. Eischeid

Raymond S Bradley

An analysis of southern hemisphere land precipitation records for the last 100 years indicates an increase in mean annual precipitation since the 1940's, with positive anomalies, compared to the 1921 - 1960 reference period, occurring during approximately the last 15 years in all seasons except southern summer (December-February). There is little or no temporal correlation with corresponding precipitation indices for the northern hemisphere (Bradley et aI., 1987a). Furthermore, while trends in the northern hemisphere temperate regions were opp'osite those in the northern tropical areas, in the southern hemisphere both zones exhibit similar trends. The change toward higher precipitation in middle …

Thermochemistry Of A Structurally Defined Aldol Reaction., Edward Arnett, Franklin Fisher, Michael Nichols, Anthony Ribeiro

Michael A Nichols

No abstract provided.

The Activation Of Carbon-Fluorine Bonds By Oxidative Addition At Tungsten(O): An Electrochemical Study, Andrea Russell, Carolyn Osterberg, Daniel Blackwood, Mark Anderson, Thomas Richmond, Stanley Pons

Mark R. Anderson

We have investigated the anodic oxidation reactions of W(CO)4Et,F5 (I), where Et,F5 is the ligand N,N'-bis(pentafluorophenylidine)ethylenediamine, by cyclic voltammetry and infrared spectroelectrochemistry. The results in both acetonitrile and methylene chloride indicate an ece type mechanism, with the product of the first electron transfer stabilized by the more coordinating solvent.

Estimating Vaporization Enthalpies Of Organic Compounds With Single And Multiple Substitution, James S. Chickos, Donald G. Hesse, Joel F. Liebman

James Chickos

No abstract provided.

Pitch Of Complex Tones With Many High‐Order Harmonics, Adrianus J. M. Houtsma, J. Smurzynski

Jacek Smurzynski

Numerical Solution Of The Eigenvalue Problem For Hermitian Toeplitz Matrices, William Trench

William F. Trench

No abstract provided.

Scattering Of Light By Stochastically Rough Particles, J.I. Peltoniemi, K. Lumme, K. Muinonen, William Irvine

William M. Irvine

The single particle phase function and the linear polarization for large stochastically deformed spheres have been calculated by Monte Carlo simulation using the geometrical optics approximation. The radius vector of a particle is assumed to obey a bivariate lognormal distribution with three free parameters: mean radius, its standard deviation and the coherence length of the autocorrelation function. All reflections/refractions which include sufficient energy have been included. Real and imaginary parts of the refractive index can be varied without any restrictions. Results and comparisons with some earlier less general theories are presented. Applications of this theory to the photometric properties of …

Dissipative Model Of The Universe, Milan Meszaros

Milan Meszaros physicist

In the present study a trial is carried out to generalize the non-relativistic-dynamic model of cosmology put forward by O. Heckmann. The generalization is performed under the framework of the Gyarmati principle of irreversible thermodynamics for anisotropic inhomogeneous and viscous case. The equation of motion of the dissipative Universe will be a Navier-Stokes tensor equation leading to a Riccatian differential equation general in one dimension. The equations of the Heckmann model compatible with standard cosmology can be obtained from this by means of further simplifying assumption.

Direct Tests Of The Rational Expectations Hypothesis: A Study Of Italian Entrepreneurs’ Inflationary Expectations (1980-1988), Claudio Lupi

Claudio Lupi

The primary concern of this paper is to test the rational expectations hypothesis for Italian entrepreneurs' inflationary expectations between 1980 and 1988 using monthly observed expectations. Particular care is devoted to analyzing the problems arising when multiperiod expectations and a nonwhite noise measurement error in the expectations series are considered. The empirical analysis is carried out using cross correlations on ARIMA residuals and transfer function models. This technique seems to be particularly appealing for rationality testing.

A Simple Monochromatic Spark Discharge Light-Source, Chin Oi Hoong

Chin Oi Hoong

Spark light illumination has been used in high-speed photog-raphy since the beginning ofthe century and various designs ofthe spark discharge light source have since been reportedr with spark duration ranging from nanoseconds to millisec-onds. We report here a simple and easy to build spark dis-charge tube for operation as a monochromatic point light source. The design and construction ofthe spark discharge tube is shown in Fig. 1. The sharp-tip solid cone anode is made of stainless steel which is screwed onto a brass rod connected A compact spark discharge tube operated as a monochromatic light source at 587.5 nm is …

Pre-1990 Articles, Stan Wagon

Stan Wagon, Retired

No abstract provided.

Polar Narcosis In Aquatic Organisms, Steven P. Bradbury, Richard W. Carlson, Tala R. Henry

Steven P. Bradbury

The majority of industrial organic chemicals lack identifiable structural characteristics that result in specific biological activity. These nonpolar-nonelectrolytes are acutely toxic to aquatic organisms via a nonspecific mode of action termed narcosis. The toxicity of industrial chemicals eliciting nonpolar narcosis can be reliably predicted by log P (baseline toxicity models). Using single chemical and joint toxic action models, several research groups have reported classes of polar compounds (for example, esters, phenols, and anilines) that elicit a narcosis-like syndrome; however, they are more acutely toxic than what is predicted using baseline toxicity models. An assessment of rainbow trout (Salmo gairdneri) in …

Comparative Toxicology Of The Pyrethroid Insecticides, Steven P. Bradbury, Joel R. Coats

Steven P. Bradbury

The toxic effects elicited by synthetic pyrethroids in animals are varied in degree and nature. Their relative safety to birds and mammals contrasts sharply with their acute effects on fish and arthropods. Explantation of their differences in toxicity depends on examination of all factors of their comparative toxicology. Routes of exposure are important, as are metabolism and elimination rates, especially for mammals and birds with their considerable capabilities for biotransformation. Significant differences in sensitivity at the sites of toxic action may also play a role in differential responses to these insecticides. Finally, physical properties that influence the environmental disposition and …

Surficial Geologic Map Of The East Cache Fault Zone, Cache County, Utah, James P. Mccalpin

James P. McCalpin

The 1:50,000-scale map shows surficial geologic deposits and the faults that displace them along the East Cache fault zone in northern Utah. The East Cache fault is a north-trending normal fault that extends about 77 km along the eastern side of Cache Valley (an east-tilted graben) at the base of the Bear River Range. The map includes a description of Quaternary deposits along the fault zone, a description of the fault segments, and estimates of the age, size, and distribution of fault scarps in the fault zone.

Intrinsic Reaction Coordinate Calculations For Very Flat Potential Energy Surfaces: Application To Singlet Si2h2 (Disilenylidene) Isomerization, Shiro Koseki, Mark S. Gordon

Mark S. Gordon

Si2H2 is an important species that may appear in the chemical vapor deposition of silicon. This paper reports an intrinsic reaction coordinate (IRC), or a minimum energy path (MEP), of the isomerization from silasilene to bridged disilyne obtained by using the local cubic and quadratic approximations. These. new approximations generate a correct IRC for this isomerization, while some conventional methods fail to predict a reasonable IRC because of the very flat potential energy surface. This reaction path bifurcates to two identical IRCs to reach bridged disilyne. The activation energy for this isomerization is predicted to be less than 3 kcalfmol. …

Transition State Structure, Barrier Height, And Vibrational Frequencies For The Reaction Cl+Ch4→Ch3+Hcl, Thanh N. Truong, Donald G. Truhlar, Kim K. Baldridge, Mark S. Gordon, Rozeanne Steckler

Mark S. Gordon

We have carried out a b i n i t i o calculations using second‐ and fourth‐order Mo/ller–Plesset perturbation theory, scaled electron correlation, and several basis sets for the reaction Cl+CH4→CH3+HCl. We found that including electron correlation is essential for obtaining accurate barrier heights and vibrational frequencies. Furthermore, scaling the correlation energy further improves the barrier height predictions provided that the basis set being used is correlation balanced for both bonds involved in the reaction. Geometries and transition state frequencies calculated at the MP2 and MP‐SAC2 levels with the most extensive and best balanced basis set are in good agreement …

Effectiveness Of Drift Fences And Tunnels For Moving Spotted Salamanders Ambystoma Maculatum Under Roads, Scott D. Jackson, T. F. Tyning

Scott D. Jackson

No abstract provided.

Relative Sea Level Chronology Determined From Raised Marine Sediments And Coastal Isolation Basins, Northeastern Ellesmere Island, Arctic Canada, Michael J. Retelle, Raymond S. Bradley, Robert Stuckenrath

Raymond S Bradley

A new relative sea level curve for the Robeson Channel area contrasts with previously published curves for the area by inferring that rapid emergence may have commenced at ca. 7400 BP, as much as 1200 yr earlier than previously predicted. Subsequently, uplift may have occurred at much lower rates from ca. 6000 BP to present. A comparison of shell dates used for the relative sea level curve and dates on disseminated total organic carbon (TOC) fractiop from lacustrine and marine sediments from sediment cores from emerged coastal lakes shows wide discrepancies. Furthermore, several inifmite TOC dates (>27,7SO to >40,600 …

On The Existence And Symmetry Properties Of Finite Total Mass Solutions Of The Matukuma Equation, The Eddington Equation And Their Generalizations, Yi Li, Wei-Ming Ni

Yi Li

No abstract provided.

Analysis Of The Potential Energy Surface Of Ar–Nh3, G. Chalasinski, S. M. Cybulski, 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–NH₃. Anisotropy of the self‐consistent field (SCF) potential is determined by the first‐order exchange repulsion. Second‐order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first‐order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second‐order correlation correction to the exchange effect is nearly as large as a half ΔE^SCF in the minimum and has a ‘‘smoothing’’ effect on the anisotropy of …

Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner

Steve Scheiner

Nonadditive effects are calculated for (HF)₃ and (HCl)₃ complexes and analyzed via the combination of perturbation theory of intermolecular forces with Møller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self‐consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three‐body terms exhibit much lesser basis set dependence than the two‐body effects and even quite moderate basis sets which are not accurate enough for treatment of two‐body forces can yield three‐body effects of quantitative quality. This is due in large measure to the …

Application Of The Batio3 Beam Fanning Limiter As An Adaptive Spatial Filter For Signal Enhancementin Pulsed Laser Excited Photothermal Spectroscopy, Stephen E. Bialkowski

Stephen E. Bialkowski

A method for obtaining a high-contrast visible-light signal from infrared absorption in low-absorbance samples is described. This method is based on a beam-fanning optical limiter in photorefractive BaTiO₃. The resulting signal is not linear but does exhibit an enhanced signal-to-background ratio that is 4 to 6 orders of magnitude better than that of conventional infrared absorption spectrophotometry in the shot-noise limit. A simple model for the beam-fanning, optical-limiter-based, pulsed-laser-excited photothermal spectroscopy detector is found to describe the experimental data adequately. This technique using photothermal spectroscopy detection may have advantages for rapid signal analysis and for two-dimensional visible imaging …

The Adiabatic Propagator, Br Holstein

Barry R Holstein

The Feynman propagator is expanded in the adiabatic limit, wherein the time scale over which the potential varies is long compared to typical quantum mechanical oscillation times in the problem. Comparison with known exact results is made for two simple models.

A Status Report On Software Quality In The United States And Japan, Robert Yacobellis

Robert H Yacobellis

No abstract provided.

Rigidity Percolation, Anthony Day, M. Thorpe, W. Xia

Anthony Roy Day

No abstract provided.

The Adiabatic Theorem And Berry's Phase, Br Holstein

Barry R Holstein

A study is presented of Berry's observation that when a quantum-mechanical system is transported on a closed adiabatic journey, a topological phase arises in addition to the usual dynamical phase expected from the adiabatic theorem. Consequences are explored in the case of a simple magnetic moment-magnetic field interaction and are shown to lead, among other things, to Dirac's famous relation between electric and magnetic charges.