Chemistry Commons^™

Esr Study Of Optically Induced Phase Transitions, Juana Vivó Acrivos, H. P. Hughes, S. S.P. Parkin

Faculty Publications, Chemistry

We have identified an optically enhanced magnetic phase transition in the newly synthesized organic molecular charge transfer salt, (BEDT-TTF)3Ta2F11 (BEDT-TTF bisethylenedithiolotetrathiafulvalene) by ESR absorption measurements in the X band microwave region. At room temperature, only a doublet state ESR absorption is observed, but below 30 K severa~ tripl~t E.SR absorpti_ons appear. The orientation dependence of the ESR absorption under lllummat10n at energies near the band gaps in the material ( 640 nm, T = 12 to 5 K H0 < 0.34 T) indicates that there are rapid spin exchange processes with times r < w-s; near 7 ~o 5 K.along cert~in ~rystallographic directions with a temperature dependen~e suggesting spm-lattlce relaxation times which proceed via Van Vleck "direct processes." This, to our knowledge, is the first case where the magnetic properties of a charge transfer salt are altered by the interaction with photons of energy equal to the band gaps in a low dimensional solid providing a new, interesting way to investigate these materials.

The Aperiodic Crystal Picture And Free Energy Barriers In Glasses, Randall W. Hall, Peter G. Wolynes

Collected Faculty Scholarship

The aperiodic crystal picture associates the glass transition with freezing into a nonperiodic structure. Dynamics in the glassy state involves activated jumps between different aperiodic free energy minima. Activation barriers may be estimated through the use of freezing theory and the theory of dense solids. The results resemble, but are distinct from, free volume theory. Reasonable fits to experimental data are obtained.

Mössbauer Spectroscopic Studies Of Hemoglobin And Its Isolated Subunits, G. R. Hoy, D. C. Cook, R. L. Berger, F. K. Friedman

Physics Faculty Publications

Samples of 90% enriched ⁵⁷Fe hemoglobin and its isolated subunits have been prepared. Mössbauer spectroscopic measurements have been made on three such samples. Sample one contained contributions of oxyhemoglobin, deoxyhemoglobin, and carbonmonoxyhemoglobin. This sample was studied from a temperature of 90 K down to 230 mK. Measurements were also made at 4.2 K using a small applied magnetic field of 1.0 T. In general, the measured quadrupole splittings and isomer shifts for each component agreed with previous measurements on single component samples in the literature, and thus demonstrated that chemically enriched hemoglobin has not been altered. The second and …

Chemical Applications Of Scanning Tunneling Microscopy, Paul West, John Kramer, David V. Baxter, Robert J. Cave, John D. Baldeschwieler

All HMC Faculty Publications and Research

The development of a scanning tunneling microscope at the California Institute of Technology is well under way. Electron tunneling has been demonstrated, and preliminary surface images of gold films have been obtained. Additional instrumental development is required to achieve the atomic resolution which is required for the study of chemical processes on surfaces. A theoretical model is also being developed for the study of tunneling of electrons from the probe to surfaces with molecular species absorbed, and with atomic and molecular species intervening between the probe and the surface. These experimental tools and theoretical models, which are being developed concurrently, …

A Theoretical Investigation Of The One– And Two–Photon Properties Of Porphyrins, Mark Masthay, Leonore A. Findsen, Brian M. Pierce, David F. Bocian, James S. Lindsey, Robert R. Birge

Chemistry Faculty Publications

The one‐ and two‐photon properties of free base porphin, free base porphin dianion, and the 2,4‐substituted diformyl and divinyl analogs of these molecules are studied using a semiempirical SCF‐MO formalism (CNDO‐π‐SCF‐MO‐PSDCI) including extensive single and double configuration interaction. Strongly two‐photon allowed states are predicted to lie in the Soret region as well as in the region between the Soret and visible bands. A number of the two‐photon allowed states in the Soret region are predicted to have two‐photon absorptivities exceeding 100×10−50 cm4 s molecule−1 photon−1. The calculations indicate that the visible (Q) states are well characterized by the …

Electrochemistry Of Dihalogenated Nicotonic Acids In Aqueous And Aprotic Media, Ali U. Shaikh, Tappi A. Dixon, Lourie A. Battles, Frank L. Setliff

Journal of the Arkansas Academy of Science

The electrochemical reduction of several 2,5- and 5,6- dihalonicotinic acids have been studied in dimethyl sulfoxide as well as in aqueous buffers of different pH. The polarographic half-wave potentials for the reduction of these compounds in both media are reported here. The compounds appear to reduce at the carboxyl group. The presence of halogen atoms on the pyridine ring facilitates reduction.

Nonadiabatic Theory Of Fine-Structure Branching Cross Sections For Na-He, Na-Ne, And Na-Ar Optical Collisions, Linda L. Vahala, P. S. Julienne, Mark D. Havey

Electrical & Computer Engineering Faculty Publications

The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na–rare-gas (RG) optical collision Na(²S_1/2)+RG+nhν μNa(²P_j)+RG+(n-1)hν. The effects of detuning and incident energy on the branching into the atomic Na 3p²P_3/2 and 3p²P_1/2 states are examined. The cross sections σ(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis …

Development Of An On-Line Computer System For Cyclic Voltammetry Studies, Tai-Lee Leo Huo

Chemistry & Biochemistry Theses & Dissertations

An Apple II Plus microcomputer was interfaced to a PAR 174A Polarographic Analyser, an HP 7O4OA X-Y recorder and a three-electrode system. This on-line computer system was applied to Cyclic Voltammetry (CV) studies. The interfacing involved both hardware and software development. Various hardware components were used to amplify and transmit the analog signal both going into the computer and coming from the computer. Software programs were written for staircase waveform generation, data acquisition, and plotting the voltammograms obtained.

A package was designed for CV experiments to be used by the students in the instrumental analysis laboratory. This package contains several …

Solvent Influence On Atomic Spectra: The Effect Of Finite Size, Randall W. Hall, Peter G. Wolynes

Collected Faculty Scholarship

Time dependent Hartree theory is used to determine the solvent effect on atomic spectra for a given solvent configuration. Configuration averaging is performed as in the mean spherical approximation, resulting in an upper bound to the polarizability. Comparisons are made with previous, more approximate theories, including path integral treatments. It is found that deviations from previous theories can be significant in certain regimes.

Thermodynamics Of Ion Association In Aqueous Fluoride Solutions. Determination Of Stability Constants For (Naf), (Mgf)+ And (Caf)+ Ion Pairs, Waldo Zamorano-Santander

Masters Theses

Stoichiometric ion-association constants were determined at several ionic strengths for (NaF) over the temperature range 15-40°C and for (MgF)⁺ and (CaF)⁺ over the temperature range 25-45°C using fluoride ion selective electrode measurements.

Thermodynamic association constants, K°, were obtained through extrapolation of the stoichiometric values to infinite dilution. Values of K° for (NaF) are 1.70, 2.16 and 2.54 at 15, 25 and 40°C, respectively. The K° values for (MgF)⁺ are 73.4, 88.0 and 98.2, and for (CaF)⁺ are 13.7, 17.5 and 21.9 at 25, 35 and 45°C., respectively.

The stoichiometric association constants for (NaF) can be reproduced …

Determination Of The Internal Rotational Energy Of Gaseous 1,2-Dichloroethane In An Argon Matrix Using Fourier Transform Spectroscopy, Susan Lynn Clarke

Chemistry & Biochemistry Theses & Dissertations

A sample cell and delivery system for rapid matrix isolation of gas mixtures at constant gas temperature was designed and evaluated. The rotational energy differences of 1,2-dichlorosthane and of its deuterium compound wars then determined to test this technique.

The rotational energy barriers calculated from Boltzman plots of ths gases at different temperatures were; 1.21 + 0.38 keel/mole, 1.33 + 0.70 Real/mole, and 1.12 + 0.45 kcal/mole for the CH2 wagging„ C-Cl stretching and CD₂ wagging modes respectively. These values were in good agreement with previously published values.

These results allowed evaluation of this apparatus and experimental design and …

Nmr Measurements On Intercalated 3r-Tas2.Ix (I=Nh3 And N2h4), N. H. Handly, Juana Vivó Acrivos

Faculty Publications, Chemistry

No abstract provided.

Mass Spectrometric Studies Of Oxygen Isotope Exchange Reactions With Oxide Surfaces, Gayle J. Allen

Chemistry & Biochemistry Theses & Dissertations

Isotopic exchange reactions with the surface of amorphous silica and crystalline quartz were studied mass spectrometrically. A mixture of approximately 2%18_o2 in neon was used as the test gas, and was passed over the surface of the oxides. Measurements were taken as a function of temperature and residence time, for kinetic studies.

These studies clearly show a second order rate law for the surfaces examined. The rate constant on amorphous silica was 2.2xl0²L/mol/sec. The energy of activation was 35.3 kcal/mol and the frequency factor was l.35xl0⁹L/mol/sec. On the crystalline quartz the rate constant was 2.0xl0 …

The Intermolecular Force Field Of Acetylene-Hcl: The Normal Coordinate And Centrifugal Distortion Analysis Of Two Weakly Bound Rigid Rods, Rebecca S. Lee

Masters Theses

In order to determine the intermolecular force field of C₂H₂⋅⋅HCl, a normal coordinate analysis appropriate for two weakly bound rigid rods is developed. An exact centrifugal distortion analysis is then carried out on the microwave spectrum of this "T''-shaped hydrogen-bonded π complex. The distortion constants and published matrix-isolated vibrational frequencies are employed in the normal coordinate analysis to obtain the intermolecular force field and refinements in the structural parameters. The following van der Waals force field is found to reproduce the existing spectroscopic constants of C₂H₂⋅⋅H³⁵Cl … . This study …

Measurement Of Low Vapor Pressures : A Kinetic Approach, Samuel Bernard Bliden

Dissertations and Theses

A kinetic model was applied to vapor pressure data obtained by a variable flow method. The vapor pressures of benzoic acid, naphthalene, benzophenone, and phenylhydrazine were measured at temperatures of 293K to 307K. The data are summarized in the data table on the following page. These data were obtained by passing air over a sample of the substance in a tube. The air stream was combusted, and a flame ionization detector was used to measure the mass of CO₂ so obtained. Several different flow rates were used at each temperature with each substance.

Xanes In (Tmtsef)2re04: Polarization Dependence Of The Se K-Edge, Juana Vivó Acrivos, S.S. P. Parkin

Faculty Publications, Chemistry

We have measured XANES (X-ray Absorption Near Edge Spectra) near the Re Li (i=l,II,III) edges in (TMTTF)2Re04 and (TMTSeF) 2Re04 and the Se K edge in the latter compound. An important dependence of the XANES at the Se K edge on the polarisation of the incident beam with respect to the crystal axes was observed, whose interpretation can give information on the symmetry of the unoccupied conduction band states. The positions of the Re L edges were compared with those in several inorganic compounds containing Re in various oxidation states, and were found to be, within experimental error, the same …

Self‐Consistent Molecular Orbital Methods. Xxiii. A Polarization‐Type Basis Set For Second‐Row Elements, Michelle M. Francl, William J. Pietro, Warren J. Hehre, J Stephen Binkley, Mark S. Gordon, Douglas J. Defrees, John A. Pople

Chemistry Faculty Research and Scholarship

The 6‐31G* and 6‐31G** basis sets previously introduced for first‐row atoms have been extended through the second‐row of the periodic table. Equilibrium geometries for one‐heavy‐atom hydrides calculated for the two‐basis sets and using Hartree–Fock wave functions are in good agreement both with each other and with the experimental data. HF/6‐31G* structures, obtained for two‐heavy‐atom hydrides and for a variety of hypervalent second‐row molecules, are also in excellent accord with experimental equilibrium geometries. No large deviations between calculated and experimental single bond lengths have been noted, in contrast to previous work on analogous first‐row compounds, where limiting Hartree–Fock distances were in …

A Laser Interferometric Study Of Electric Field Effects On Methane-Oxygen Flame Plasmas, Mark D. Prairie

Masters Theses

A laser interferometer is developed to study the refractive index field, aerodynamic structure, and three dimensional temperature profile of a methane-oxygen flame system under the influence of D.C. electric fields. A combined graphical-numerical method is used to transform the observed interference patterns into radial temperature distributions. The results indicate that the electric field exerts a marked influence on the flame stability, geometry, and charged particle flow. Experimental evidence shows that these effects are most apparent under fuel rich conditions. It is suggested an electric field may change the concentration gradients of reacting species, leading to an altered course of fuel …

Measurement Of Synchrotron X-Ray Energies And Line Shapes Using Diffraction Markers, Juana Vivó Acrivos, S.S. P. Parkin, K. Hathaway, J. R. Reynolds, M. P. Klein, A. Thompson, D. Goodin

Faculty Publications, Chemistry

Standard reference markers for accurate, reproducible synchrotron x-ray energies are obtained using a three Si crystal spectrometer. The first two crystals are in the monochromator and the third is used to obtain diffraction markers which monitor the energy. Then for any value of the glancing angle on the reference Si crystal the energy for the (333) diffraction must occur at 3/4 that of the (444) and 3/5 of that for the (555). This establishes for the first time an absolute synchrotron energy scale. Higher-order diffractions are used to determine excitation line profiles. We conclude that the use of reference diffractions …

Isolation And Characterization Of Frullanolide From Frullania Franciscana (Howe), Marshall Stuart Sass

Dissertations and Theses

Investigation of the ether extract of the liverwort Frullania franciscana (Howe) resulted in the isolation of the sesquiterpene lactone frullanolide. The separation techniques of thin-layer chromatography, dry column chromatography, and liquid column chromatography were evaluated. Only liquid column chromatography was found useful. Fractions from alumina liquid column separations had infrared spectra which resembled the published spectrum of frullanolide. The identity of the compound obtained from F. franciscana (Howe) was established after extensive purification by comparison of its infrared and nuclear magnetic resonance spectra with published spectra of frullanolide.

Effects Of N2h4 On The Transition Temperature In The Anisotropic Superconductor Tase3, K. Yamaya, T. H. Geballe, Juana Vivó Acrivos, J. Code

Faculty Publications, Chemistry

No abstract provided.

Mott G-Ratios In Rbx(Nh3)1-X And Oxidation State Of Rubidium Compounds From Xas, Juana Vivó Acrivos, K. Hathaway, A. Robertson, M. P. Klein, A. Thompson

Faculty Publications, Chemistry

The x-ray absorption spectra (XAS) of Rb metal, Rh,("JH,J, ,, 2H-NbSe2Rb111x and RbBr near the Rb K-edge have been used to ascertain that the oxidation state V of rubidium dissolved in ammonia and intt:rcalated in the layer compound is in the range 0 < V < I. Theobservededge shifts with temperature for semimctals are explainedin terms of the population of band states, and the ratio of the density states near the mobility edge over that calculated for a free electron model, i.e. the Mott ratio g, is ascertained using a semiempirical relation developed for the x-ray absorbance from Is levels to empty states ncar the mobility edge.

Conduction Band Symmetry In Ta Chalcogenides From Ta L Edge X-Ray Absorption Spectroscopy (Xas), Juana Vivó Acrivos, S.S. P. Parkin, J. Code, J. Reynolds, K. Hathaway, H. Kurasaki, E. Marseglia

Faculty Publications, Chemistry

No abstract provided.

Spectroscopic Studies Of Pre-Mixed Hydrocarbon Flame Plasmas, Tsao-Chin C. Huang

Masters Theses

This thesis contains two different studies.

Chapter 1, "Infrared Emission Spectrum of the Hydroxyl Radical.", is in collaboration with Dr. Giles L. Henderson and Mr. Chun-Sheng Ko. This chapter has been submitted and accepted for publication by the Journal of Chemical Education.

In this chapter, we describe a rather novel physical chemistry experiment in which ab initio potential parameters for the OH radical are compared with those obtained from the ir emission spectrum of an oxy-acetylene welding torch.

Chapter 2, "A Preliminary Spectroscopic Study of Field-Induced Ion Movements in Flame Gases.", describes the effects of longitudinal electric fields on CH …

The Use Of Thermal Analysis In The Identification And Characterization Of Fibers Of Forensic Interest, Ronald J. Coffey

All-Inclusive List of Electronic Theses and Dissertations

This study investigates the use of thermal analysis for the identification and characterization of fibers for forensic purposes. Fibers such as polyesters, polyacrylics, polypropylenes and nylon were investigated by Differential Thermal Analysis (D.T.A.) and Thermogravimetric Analysis (T.G.A.) to see if their resulting thermograms were characteristic of each fiber. Also, infrared analysis was performed on each fiber. In addition, such factors as heating rate and sample size along with fiber blends were studied as to their effect on thermograms. As a result of this study several important conclusions may be drawn. Although it was found that for the most part D.T.A. …

Synthesis And Reactivity Of Some Fe(0) And Ru(0) Compounds, Michael E. Hawkins

Masters Theses

The catalytic activity of the compounds used in this study, Ru[P(C₆H₅)₃]₄ (η²-CH₃CN)⋅CH₃CN, Ru(CO)[P(C₆H₅)₃]₃CH₃CN, Ru(CO)₂[P(C₆H₅)₃]₃, Fe(CO)₂[P(C₆H₅)₃]₃ was compared using the isomerization of allylbenzene to β-methylstyrene as the test reaction. The measured decreasing order of reactivity for these complexes is: Ru(CO)[P(C₆H₅)₃]₃CH₃CN > Ru[P(C₆H₅)₃]₄ (η …

A Numerical Method For The Solution Of The Schrödinger Equation By A Trial Wavefunction Improvement Formula, Chun-Sheng Ko

Masters Theses

A numerical method and corresponding computer algorithm for solving the one-dimensional radial Schrödinger equation to any desired accuracy is developed. The method uses a finite difference scheme in which an initial trial wavefunction is digitalized over a lattice covering the region of integration. The values of a rough solution are then altered at each lattice point by a simple improvement formula decreasing the value of the variational energy until the desired minimum is reached. The accuracy of these solutions depends only on the grid size. This method is characterized and tested with a harmonic oscillator potential. Practical evaluations and applications …

Analytical Applications Of Ultrasonic Velocity Using Three-Transducer Phase-Shift Detection, Chuan Chen

Chemistry and Chemical Biology ETDs

A new method for determining ultrasonic velocity and its appli­cation as a high-performance liquid chromatography (H.P.L.C.) detector is developed. The method involves in using a three­transducer phase-shift device where two transducers alternately transmit 1-MHz continuous wave signals to the same receiver. Ultra­sonic velocity can be calculated from the phase-shift difference between the two cell paths. When the device is used as an H.P.L.C. detector, the reciprocal of the phase-shift difference between the two cell paths is converted to an electrical signal and recorded on a chart paper with respect to retention time. The theoretical principles are discussed and the appropriate …

Site Specificity In The Intercalation Of Antitumor Antibiotics With Dna, Martin Bradford Jones

Chemistry and Chemical Biology ETDs

Many planar molecules or molecules with planar moieties have been shown to bind to DNA by intercalation, which can be defined as the insertion of a planar moiety between adjacent bases on the DNA strand, reading in the 3'-5' direction, accompanied by a partial unwinding and elongation of the helix in the immediate vicinity of the intercalation site. Intercalation raises the question of specificity of binding of the drug to DNA, since there are 16 possible intercalation sites in normal double-stranded DNA. The conformational changes (elongation and unwinding) associated with intercalation make circular dichroism (CD) an excellent technique for studying …

The Synthesis Of C₄ And C₅ 13c-Labeled Benzo[A]Pyrene, Benzo[A]Pyrene-4, 5-Oxide And Derivatives. Studies Of The Reactions Of Benzo[A]Pyrene-4, 5-Oxide Using 13cnmr, Mark David Hylarides

Chemistry and Chemical Biology ETDs

Benzo[a]pyrene (BAP), BAP-4,5-oxide, and other derivatives which are 13c-labeled in the 4-and 5-positions were synthesized. The synthetic scheme involves an initial reaction of the lithioenolate of ethyl acetate-1-13c or ethyl acetate-2-13c with l,2-dihydrochrysen4(3H)-one. Subsequent dehydration and dehydrogenation gave ethyl 4-chryseneacetate-1-C (or 2-C). Partial reduction to the aldehyde 13 13 followed by cyclization gave BAP-5-C (and 4-C). Toe synchesis of 13 BAP-4,5-oxide-4-13c (and 5-c) involved saponification of ethyl 4-chryseneacetate-1-13c (and 2-13c), an intermediate in the synthesis of BAP, followed by cyclization of the resultant acid to BAP-5-ol13 s-c (and 4-13c). The crude phenol was oxidized to the o-quinone. Further reduction of …