Chemistry Commons^™

Reactions Of Aqueous Chlorine With Valine In Model Solutions And In Wastewater, Erika Forrer Mccormick

Chemistry & Biochemistry Theses & Dissertations

Solutions of the amino acid valine were chlorinated to seven chlorine-to-nitrogen mole (Cl/N) ratios and analyzed by high performance liquid chromatography, gas chromatography/mass spectroscopy, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The chlorination products found were N-chlorovaline, isobutyraldehyde, isobutyronitrile, and N-chloroisobutyraldimine. Their product distribution depends on the level of chlorination and pH. The main products identified at the lower CI/N mole ratios were N-chlorovaline and isobutyraldehyde, whereas at the higher CI/N mole ratios isobutyronitrile and N-chloroisobutyraldimine were identified as the main products. The concentration and the chlorination products of valine in municipal wastewater were also determined. The chlorination products of …

Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin

Chemistry and Biochemistry Faculty Research

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He⁺⁺/He⁺=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.

Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan

Chemistry and Biochemistry Faculty Research

Strongly anisotropic, polarized Cl K-V x-ray emission from gas-phase CF₃Cl has been observed following resonant excitation with a linearly polarized x-ray beam. Distinctively different angular distributions are observed for x-ray emission involving molecular orbitals of different symmetries. A classical model of the x-ray absorption-emission process accurately describes the observed radiation patterns.

A Diffuse Reflectance Infrared Fourier Transform Spectroscopic Study Of Platinum/Tin (Iv) Oxide Low-Temperature Carbon Monoxide Oxidation Catalysts, Donna Sue Duarte

Chemistry & Biochemistry Theses & Dissertations

Platinum-coated tin(IV) oxide catalysts have been developed for the recombination of carbon monoxide and oxygen at 55°C and 1 atmosphere of pressure in closed-cycle carbon dioxide lasers. A diffuse reflectance infrared fourier transform spectroscopic (DRIFTS) study of four of these catalysts during 5% carbon monoxide pretreatment at temperatures of 30°C, 100°c, 125°c, and 150°C has been performed. Evidence for the development of surface carbonate, bicarbonate, and formate species during pretreatment has been found. Dehydroxylation of the surface and loss of a partially charged hydrogen-bonded hydroxyl species have also been found to result from elevated temperature pretreatment. The four catalysts have …

Nonlinear Optical Properties Of Bacteriorhodopsin: Assignment Of The Third-Order Polarizability Based On Two-Photon Absorption Spectroscopy, Robert R. Birge, Mark Masthay, Jeffery A. Stuart, Jack R. Tallent, Chian-Fan Zhang

Chemistry Faculty Publications

The third-order (pi) -electron polarizability, (gamma) (pi), of bacteriorhodopsin in the 0.0 - 1.2 eV optical region is assigned based on an analysis of the experimental two-photon properties of the low-lying singlet state manifold. The following selected values of (gamma) (pi) (units of 10-36 esu) are observed: (gamma) (0;0,0,0) equals 2482 +/- 327; (gamma) (-3(omega) ;(omega) ,(omega) ,(omega) ) equals 2976 +/- 385 ((omega) equals 0.25 eV), 5867 +/- 704 ((omega) = 0.5 eV), 14863 +/- 1614 ((omega) = 0.66 eV), 15817 +/- 2314 ((omega) equals 1.0 eV), 10755 +/- 1733 ((omega) equals 1.17 eV). The third-order polarizability of this …

Molecular-Orbital Studies Via Satellite-Free X-Ray Fluorescence: Cl-K Absorption And K–Valence-Level Emission Spectra Of Chlorofluoromethanes, Rupert C. Perera, P. L. Cowan, Dennis W. Lindle, R. E. Lavilla, T. Jach, R. D. Deslattes

Chemistry and Biochemistry Faculty Research

X-ray absorption and emission measurements in the vicinity of the chlorine K edge of the three chlorofluoromethanes have been made using monochromatic synchrotron radiation as the source of excitation. By selectively tuning the incident radiation to just above the Cl 1s single-electron ionization threshold for each molecule, less complex x-ray-emission spectra are obtained. This reduction in complexity is attributed to the elimination of multielectron transitions in the Cl K shell, which commonly produce satellite features in x-ray emission. The resulting "satellite-free" x-ray-emission spectra exhibit peaks due only to electrons in valence molecular orbitals filling a single Cl 1s vacancy. These …

Nonadiabatic Electronic Interactions In The Ion-Pair States Of Nelcl, Thomas Alex Stephenson, Y. Hong, M. I. Lester

Chemistry & Biochemistry Faculty Works

Nonadiabatic interactions in the NeIC1 van der Waals complex have been explored in the lowest energy triad of IC1 ion-pair states (approximately 39 000 cm-1). Dispersed fluorescence measurements reveal emission characteristic of multiple ion-pair electronic states, with the relative contributions from the E(O+ ), beta(1), and D'(2) states changing with the initial IC1 vibrational excitation (v(IC1)). Emission directly from NeIC1 (v(IC1) = O) complexes indicates that the initially prepared NeIC1 levels have mixed electronic character and that the IC1 electronic parentage changes with the initial van der Waals vibrational level selected. NeIC1 complexes prepared with 1-4 quanta of IC1 stretch …

Polarized X-Ray-Emission Studies Of Methyl Chloride And The Chlorofluoromethanes, Dennis W. Lindle, P. L. Cowan, T. Jach, R. E. Lavilla, R. D. Deslattes, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

A new technique sensitive to molecular orientation and geometry, and based on measuring the polarization of x-ray emission, has been applied to the Cl-containing molecules methyl chloride (CH₃Cl) and the chlorofluoromethanes (CF₃Cl, CF₂Cl₂, and CFCl₃) in the gas phase. Upon selective excitation using monochromatic synchrotron radiation in the Cl K-edge (Cl 1s) near-threshold region, polarization-selective x-ray emission studies reveal highly polarized molecular valence x-ray fluorescence for all four molecules. The degree and the orientation of the polarized emission are observed to be sensitive to the incident excitation energy near …

High-Resolution Photoelectron Spectrometry Study Of Conjugate Shakeup Processes In The Li 1s Threshold Region, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the ¹P and ³P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the ¹P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the ³P satellite correctly.

Development, Justification, And Use Of A Projection Operator In Path Integral Calculations In Continuous Space, Randall W. Hall, Melissa R. Prince

Collected Faculty Scholarship

A projection operator, similar to one previously used by us for problems with a finite set of basis functions, is suggested for use with continuous basis sets. This projection operator requires knowledge of the nodes of the density matrix at all temperatures. We show that a class of nodes, determined from the noninteracting density matrix and present at high temperatures in the interacting system are preserved to first order in the interaction at low temperatures. While we cannot show that the nodes are present at intermediate temperatures, we suspect they do exist and, as a test of this conjecture, we …

Path Integral Studies Of The 2d Hubbard Model Using A New Projection Operator, Randall W. Hall

Collected Faculty Scholarship

Feynman’s path integral formulation of quantum mechanics, supplemented by an approximate projection operator (exact in the case of noninteracting particles), is used to study the 2D Hubbard model. The projection operator is designed to study Hamiltonians defined on a finite basis set, but extensions to continuous basis sets are suggested. The projection operator is shown to reduce the variance by a significant amount relative to straightforward Monte Carlo integration. Approximate calculations are usually within one standard deviation of exact results and virtually always within two to three standard deviations. In addition, the algorithm scales with the number of discretization points …

Hydrogen Sulfide And Radon In And Over The Western North Atlantic Ocean, T. W. Andreae, Gregory A. Cutter, N. Hussain, J. Radford-Knoery, M. O. Andreae

OES Faculty Publications

Atmospheric measurements of radon and hydrogen sulfide, and seawater measurements of total sulfide, free sulfide, and carbonyl sulfide, were made on a cruise in the western North Atlantic Ocean (October 24 to November 9, 1989). Measured values for ²²²Rn ranged from 3 to 70 pCi m⁻³, those for atmospheric hydrogen sulfide from 1 to 85 parts per trillion, and those for dissolved total and free sulfide in seawater from 33 to 930 pmol L⁻¹ and 0 to 73 pmol L⁻¹, respectively. A positive correlation between ²²²Rn and atmospheric H₂S was observed. …

Direct Determination Of Molecular-Orbital Symmetry Of H2s Using Polarized X-Ray Emission, R. Mayer, Dennis W. Lindle, S. H. Southworth, P. L. Cowan

Chemistry and Biochemistry Faculty Research

X-ray emission from the molecule H₂S is strongly polarized following excitation of a sulfur K-shell electron to an unoccupied subthreshold molecular orbital with a polarized x-ray beam. Changes in the polarization of the emission spectrum are observed as the incident beam's energy is swept across the subthreshold absorption resonance. The previously unresolved absorption resonance is shown experimentally to be primarily associated with a molecular orbital of b₂ symmetry, but with a high-excitation-energy component due to an orbital with a₁ symmetry. Satellite emission intensity is shown to depend on the primary photon energy and is therefore associated …

Second Coefficient Of Viscosity In Air, Robert L. Ash, Allan J. Zuckerwar, Zhonquan Zheng

Mechanical & Aerospace Engineering Faculty Publications

Acoustic attenuation measurements in air were analyzed in order to estimate the second coefficient of viscosity. Data over a temperature range of 11 C to 50 C and at relative humidities between 6 percent and 91 percent were used. This analysis showed that the second coefficient of viscosity varied between 1900 and 20,000 times larger than the dynamic or first coefficient of viscosity over the temperature and humidity range of the data. In addition, the data showed that the molecular relaxation effects, which are responsible for the magnitude of the second coefficient of viscosity, place severe limits on the use …

Interaction Of Pyridine With Ba2casr2cu20x, Juana Acrivos, C. Lin

Faculty Publications, Chemistry

The adsorption of of pyridine on single crystals of Bi2CaSr2Cu2Ox has been followed by optical microscopy on the crystal surface, where a blue solution is formed as a first step of reaction. The superconducting properties of the single crystal and its structure were monitored by ac susceptibility and by x-ray diffraction measurements. The results (as observed by the growth of the blue solution boundary versus time with Daa = 3.7x10-10 cm2/s.) indicate that the reaction starts at nucleation sites on the basal surface of the crystal. The edges of the crystal also show blue nucleation sites but these do not …

Role Of Surface Morphology In Wafer Bonding, W.P. Maszara, B.L. Jiang, A. Yamada, G.A. Rozgonyi, H. Baumgart, A.J.R. De Kock

Electrical & Computer Engineering Faculty Publications

The strain patterns detected by x-ray topography in wafers bonded for silicon-on-insulator (SOI) technology were found related to the flatness nonuniformity of the original wafers. Local stresses due to the bonding process are estimated to be about 1×10⁸ dynes/cm². The stress is reduced about 100 times for the thin (0.5 μm) SOI films. Most of the wafer deformation occurs during room temperature mating of the wafers. The deformation is purely elastic even at 1200 °C. The magnitude of the stress appears insignificant for complimentary metal-oxide-semiconductor devices performance.

Argon-Photoion–Auger-Electron Coincidence Measurements Following K-Shell Excitation By Synchrotron Radiation, Jon C. Levin, C. Biedermann, N. Keller, L. Liljeby, C.-S. O, R. T. Short, Ivan A. Sellin, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Argon photoion spectra have been obtained for the first time in coincidence with K-LL and K-LM Auger electrons, as a function of photon energy. The simplified charge distributions which result exhibit a much more pronounced photon-energy dependence than do the more complicated noncoincident spectra. In the near-K-threshold region, Rydberg shakeoff of np levels, populated by resonant excitation of K electrons, occurs with significant probability, as do double-Auger processes and recapture of the K photoelectron through postcollision interaction.

A Potentiometric Gaseous Hydrogen Sensor, Anne Guillory

Chemistry & Biochemistry Theses & Dissertations

The development of a potentiometric gaseous hydrogen sensor using a 75% palladium - 25% silver alloy as a selectively hydrogen permeable electrode is described. The sensor showed some promise when used with a molten base electrolyte. Other electrolytes are investigated at ambient and higher temperatures. Various cell designs including a platinum/silver-silver chloride sensor with a gel electrolyte are discussed.

The Reaction Of Organoboranes With N-Chloro-N-Sodiocarbamates: A Convenient Synthesis Of N-Alkylcarbamates, Nanette M. Wachter-Jurcsak

Chemistry & Biochemistry Theses & Dissertations

N-alkylcarbamic acid esters are used extensively as fungicides, herbicides and pesticides. Industrial methods of preparation employ highly toxic reagents in their synthesis. Convenient and safe alternative methods are necessary.

Organoboranes are electrophilic compounds which can be employed as a source of alkyl substituents. They have been shown to successfully transfer alkyl groups to the nitrogen of chloramines. N-Alkylation of carbamic acid esters by reacting the corresponding N-chloro-N-sodiocarbamate with a variety of trialkylboranes is described. The yields of the various N-substituted products are discussed.

Two synthetic methods were devised. Originally, an equivalent of the isolated N-chlorocarbamate salt was added to the …

A Pulse Gas Chromatographic Method For Determining The Dispersion And Surface Area Of Co Oxidation Catalysts, Susan Kay Ohorodnik

Chemistry & Biochemistry Theses & Dissertations

Catalysts composed of platinum and/or palladium on tin(IV) oxide supports with or without silica gel have been developed for the recombination of carbon monoxide and oxygen to form carbon dioxide for use in carbon dioxide lasers. A pulse gas chromatographic method has been developed to measure the chemisorption properties of the catalysts. From the chemisorption measurements, the active surface area and dispersion of the catalysts have been determined.

Evaluation Of The Function Exp (X2) Erfc (X) To Higher Precisions For Higher-Order Derivative Polarography Of Ce-Type Electrode Process, Myung-Hoon Kim, Veriti P. Smith, Tae-Kee Hong

Chemistry & Biochemistry Faculty Publications

The function exp(x2)erfc(x), which is often encountered in studies of electrode kinetics, is evaluated to an extended precision with 32 significant decimal digits in order to find theoretical relationships used in derivative polarography/voltammetry for a chemically-coupled electrode process. Computations with a lower precision are not successful. Evaluation of the function is accomplished by using three types of expansions for the function. Best ranges of arguments are selected for each equation for particular precisions for efficiencies. The method is successfully applied to calculate higher-order derivatives of the current-potential curves in all potential ranges for a reversible electron transfer reaction coupled with …

Path Integral Study Of The Correlated Electronic States Of Na4–Na6, Randall W. Hall

Collected Faculty Scholarship

Feynman’s path integral formulation of quantum mechanics is used to study the correlated electronic states of Na4–Na6. Two types of simulations are performed: in the first, the nuclei are allowed to move at finite temperature in order to find the most stable geometries. In agreement with previous calculations, we find that planar structures are the most stable and that there is significant vibrational amplitude at finite temperatures, indicating that the Born–Oppenheimer surface is relatively flat. In the second type of simulation, the nuclei are held fixed at symmetric and asymmetric geometries and the correlated electron density is found. Our results …

Origins Of The Quantum Efficiency Duality In The Primary Photochemical Event Of Bacteriorhodopsin, Robert R. Birge, Leonore A. Findsen, Albert F. Lawrence, Mark Masthay, Chian-Fan Zhang

Chemistry Faculty Publications

Experimental and theoretical evidence is presented which suggests that two distinct forms of light-adapted bacteriorhodopsin may exist. We propose that these two forms have characteristic photocycles with significantly different primary quantum yields. INDO-PSDCI molecular orbital procedures and semiempirical molecular dynamics simulations predict that one ground state geometry of bR undergoes photochemistry with a primary quantum yield, Φ1, of ~ 0.27, and that a second ground state geometry, with a slightly displaced counterion, yields Φ1 ~ 0.74. This theoretical model is supported by the observation that literature measurements of Φ1 tend to fall into one of two categories- those that observe …

The Spectroscopy And A State Dynamics Of The Neibr Van Der Waals Complex, William Robert Simpson , '88, Thomas Alex Stephenson

Chemistry & Biochemistry Faculty Works

The A  3Π1←X  1Σ+ laser‐induced fluorescence excitation spectrum of the NeIBr van der Waals complex is reported and analyzed to extract information regarding the structure and vibrational predissociation dynamics of the complex. While no definitive geometric information regarding NeIBr is obtained, our data indicate that a linear geometry is at least plausible. The vibrational predissociation lifetimes are a strong function of A state vibrational level and range from 2.6 to 23 ps. The variation in lifetime with vibrational level is consistent with the results of previous measurements on rare gas–halogen complexes, particularly NeBr2.

The Exchange Potential In Path Integral Studies: Analytical Justification, Randall W. Hall

Collected Faculty Scholarship

We present analytical justification for our previously described exchange pseudopotential. We show how the fermi quantum partition function can be constructed from the Boltzmann (distinguishable particle) wave functions if the states that correspond to like‐spin electrons occupying the same quantum state are excluded. A class of weighting functions that satisfy this constraint approximately is discussed. Our previous pseudopotential falls under this class. Essentially, our pseudopotential forces the unwanted states to have high energy and, hence, to make negligible contribution to the partition function. Exchange potentials of the form discussed in this article should be useful for studying systems where the …

Friedrich Wöhler, John Alfred Heitmann

History Faculty Publications

Friedrich Wöhler synthesized urea in 1828 and thus first demonstrated that organic materials, heretofore believed to possess a vital force, need not be made exclusively within living organisms. He also isolated aluminum metal in 1827 and discovered the elements beryllium and yttrium.

Dynamics Of Chain Molecules, Walter H. Stockmayer

DSLS 1988-1989

(Abstract taken from the Distinguished Scientist Lecture Series Program 1988-1989).

The recording of lecture not available.

Dr. Stockmayer is the Albert W. Smith Professor Emeritus at Dartmouth College, a position he has held since 1979. In 1935, Dr. Stockrnayer graduated from Massachusetts Institute of Technology. After two years at Oxford University, he returned to M.1.T. and earned his Ph.D. degree in 1940. His thesis, directed by James A. Beattie, was on the equation of state of gas mixtures. Dr. Stockrnayer became an Instructor in Chemistry at M.I.T. in 1939. Except for a two-year stint at Columbia University, he taught at …

Low Pressure Gas Flow Analysis Through An Effusive Inlet Using Mass Spectrometry, David Robert Brown

Chemistry & Biochemistry Theses & Dissertations

A mass spectrometric method for analyzing flow past and through an effusive inlet designed for use on the tethered satellite and other entering vehicles is discussed. Source stream concentrations of species in a gaseous mixture are determined using a calibration of measured mass spectral intensities versus source stream pressure for standard gas mixtures and pure gases. Concentrations are shown to be accurate within experimental error. Theoretical explanations for observed mass discrimination effects as they relate to the various flow situations in the effusive inlet and the experimental apparatus are discussed.

The Treatment Of Exchange In Path Integral Simulations Via An Approximate Pseudopotential, Randall W. Hall

Collected Faculty Scholarship

An approximate form that includes the effects of exchange is suggested for the short time propagator used in path integral simulations. The form is inspired physically by the approximation made in Hartree–Fock treatments of atoms and molecules. The approximate propagator is used with q u a n t i t a t i v e accuracy in two systems: an ideal gas of fermions localized in a three‐dimensional harmonic well and the triplet state of the sodium dimer.

Gas Permeation Measurements On Small Polymer Specimens, Karen S. Burns

Chemistry & Biochemistry Theses & Dissertations

Mass spectrometry was used to measure oxygen and nitrogen permeabilities while polarography was used to measure oxygen permeabilities for several contact lens materials. Applicable sample holders were designed and fabricated to accommodate curved and flat specimens with surface areas of 0.5 cm² and 1.0 cm² and thicknesses between 0.025 mm and 0.500 mm. A prepared standard was used to calibrate the mass spectrometric analyses.

The oxygen permeability values determined by mass spectrometry were significantly greater than those determined by polarography. This was attributed to the phase boundary phenomena and the limiting oxygen permeance of water inherent in the …