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Seventh international conference on time-resolved vibrational spectroscopy

Description: The International Conference on Time-Resolved Vibrational Spectroscopy (TRVS) is widely recognized as the major international forum for the discussion of advances in this rapidly growing field. The 1995 conference was the seventh in a series that began at Lake Placid, New York, 1982. Santa Fe, New Mexico, was the site of the Seventh International Conference on Time-Resolved Vibrational Spectroscopy, held from June 11 to 16, 1995. TRVS-7 was attended by 157 participants from 16 countries and 85 institutions, and research ranging across the full breadth of the field of time-resolved vibrational spectroscopy was presented. Advances in both experimental capabilities for time-resolved vibrational measurements and in theoretical descriptions of time-resolved vibrational methods continue to occur, and several sessions of the conference were devoted to discussion of these advances and the associated new directions in TRVS. Continuing the interdisciplinary tradition of the TRVS meetings, applications of time-resolved vibrational methods to problems in physics, biology, materials science, and chemistry comprised a large portion of the papers presented at the conference.
Date: April 1, 1997
Creator: Dyer, R.B.; Martinez, M.A.D.; Shreve, A. & Woodruff, W.H.
Partner: UNT Libraries Government Documents Department

Vibrational and electronic transition in InAs quantum dots formed by sequential implantation of In and As in a-SiO[sub 2]

Description: Optical, structural, and thermodynamic properties of materials can be changed by reducing their dimensions. We sequentially implanted In and As into fused silica windows in order to investigate formation and properties of InAs nano-particles. UV/VIS/NIR, FTIR in mid-IR, and far-IR spectroscopy were used to study change in electronic transitions and in vibrational modes (phonons) of the nano-particles InAs. The phonons can be confined to the surface of nano-particles and have frequencies falling between the transverse and longitudinal optical modes of the bulk material. Thermal annealing developed the formation of InAs quantum dots from as-implanted In-As system. At certain annealing temperature a change in UV/VIS transmission spectra and IR reflectance spectra indicated formation of InAs quantum dots. This is particularly evident from the absorption in IR and surface phonon bands are observed, confirming presence of quantum confined InAs.
Date: January 1, 1996
Creator: Ueda, A.; Henderson, D.O.; Mu, R.; Tung, Y.S.; Hall, C.; Zhu, J.G. et al.
Partner: UNT Libraries Government Documents Department

Natural materials for carbon capture.

Description: Naturally occurring clay minerals provide a distinctive material for carbon capture and carbon dioxide sequestration. Swelling clay minerals, such as the smectite variety, possess an aluminosilicate structure that is controlled by low-charge layers that readily expand to accommodate water molecules and, potentially, carbon dioxide. Recent experimental studies have demonstrated the efficacy of intercalating carbon dioxide in the interlayer of layered clays but little is known about the molecular mechanisms of the process and the extent of carbon capture as a function of clay charge and structure. A series of molecular dynamics simulations and vibrational analyses have been completed to assess the molecular interactions associated with incorporation of CO2 in the interlayer of montmorillonite clay and to help validate the models with experimental observation.
Date: November 1, 2010
Creator: Myshakin, Evgeniy M. (National Energy Technology Laboratory, Pittsburgh, PA); Romanov, Vyacheslav N. (National Energy Technology Laboratory, Pittsburgh, PA) & Cygan, Randall Timothy
Partner: UNT Libraries Government Documents Department

Octupole and hexadecapole bands in 152Sm

Description: The nucleus {sup 152}Sm is characterized by a variety of low-energy collective modes, conventionally described as rotations, {beta} vibrations, and {gamma} vibrations. Recently, it has been suggested that {sup 152}Sm is at a critical point between spherical and deformed collective phases. Consequently, {sup 152}Sm is being studied by a variety of techniques, including radioactive decay, multi-step Coulomb excitation, in-beam ({alpha},2n{gamma}) {gamma}-ray spectroscopy, and (n,n'{gamma}) spectroscopy. The present work focuses on the latter two reactions; these have been used to investigate the low-lying bands associated with the octupole degree of freedom, including one built on the first excited 0{sup +} band. In addition, the K{sup {pi}} = 4{sup +} hexadecapole vibrational band has been identified.
Date: May 13, 2005
Creator: Garrett, P E; Kulp, W D; Wood, J L; Bandyopadhyay, D; Christen, S; Choudry, S et al.
Partner: UNT Libraries Government Documents Department

Quantum effects in unimolecular reaction dynamics

Description: This work is primarily concerned with the development of models for the quantum dynamics of unimolecular isomerization and photodissociation reactions. We apply the rigorous quantum methodology of a Discrete Variable Representation (DVR) with Absorbing Boundary Conditions (ABC) to these models in an attempt to explain some very surprising results from a series of experiments on vibrationally excited ketene. Within the framework of these models, we are able to identify the experimental signatures of tunneling and dynamical resonances in the energy dependence of the rate of ketene isomerization. Additionally, we investigate the step-like features in the energy dependence of the rate of dissociation of triplet ketene to form {sup 3}B{sub 1} CH{sub 2} + {sup 1}{sigma}{sup +} CO that have been observed experimentally. These calculations provide a link between ab initio calculations of the potential energy surfaces and the experimentally observed dynamics on these surfaces. Additionally, we develop an approximate model for the partitioning of energy in the products of photodissociation reactions of large molecules with appreciable barriers to recombination. In simple bond cleavage reactions like CH{sub 3}COCl {yields} CH{sub 3}CO + Cl, the model does considerably better than other impulsive and statistical models in predicting the energy distribution in the products. We also investigate ways of correcting classical mechanics to include the important quantum mechanical aspects of zero-point energy. The method we investigate is found to introduce a number of undesirable dynamical artifacts including a reduction in the above-threshold rates for simple reactions, and a strong mixing of the chaotic and regular energy domains for some model problems. We conclude by discussing some of the directions for future research in the field of theoretical chemical dynamics.
Date: December 1, 1995
Creator: Gezelter, J.D.
Partner: UNT Libraries Government Documents Department

Lattice dynamics of LuPO{sub 4}

Description: Lutetium orthophosphate is an important nonmagnetic host material for rare-earth-activated luminescence applications. We have measured the LuPO{sub 4} phonon density of states and dispersion curves along the [{xi}00],[{xi}{xi}0], and [00{xi}] symmetry directions by neutron spectroscopy using polycrystalline and single-crystal samples. A quantitative analysis of the neutron results was carried out using a lattice-dynamical shell model.
Date: June 1996
Creator: Nipko, J. C.; Loong, C.-K.; Loewenhaupt, M.; Reichardt, W.; Braden, M. & Boatner, L. A.
Partner: UNT Libraries Government Documents Department

Photodissociation of ketene: CH{sub 2}CO {yields} CH{sub 2}(a{sup 1}A{sub 1}) + CO(v=1) rates and dynamics

Description: The rotational energy release in the dissociation of ketene (CH{sub 2}CO) along its singlet potential energy surface is observed and compared with several statistical and dynamical theories. Rotational distributions for the product, CO(X{sup 1}{Sigma}+)(v=1), are measured from the threshold for production of CH{sub 2}(a {sup 1}A{sub 1}) (0,0,0) + CO(X{sup 1}{Sigma}+)(v=1) to 1720 cm{sup -1} above. Near threshold (E{le} 200 cm{sup -1} over threshold), phase space theory (PST) matches the observed distributions. At 357 and 490 cm{sup -1}, PST constrained by the measured state distributions of the methylene fragment, provides a good fit to these CO(v=1) rotational distributions. For E > 490 cm{sup -1}, the constrained PST matches the average rotational energy observed but predicts distributions which are broader than observed. This contrasts to the rotational distributions of the {sup 1}CH{sub 2} fragment which become shifted to lower rotational states than PST as energy increases from 200 cm{sup -1} above threshold. Dynamical models, the impulsive model and Franck-Condon mapping, do not account for the product rotational state distributions. The CO(v=1) rotational distributions for E > 200 cm{sup -1} contain no measurable product from triplet channel fragmentation. Therefore, they can be compared with the previously determined CO(v=0) rotational distributions in order to partition the CO(v=0) yield between singlet and triplet channels and recalculate the singlet yield. This new yield is found to be at the upper limits of the range previously reported. Rate constants and quantum yields have been determined for the photodissociation of ketene to produce CH{sub 2}(a {sup 1}A{sub 1}) (0,0,0) + CO(X {sup 1}{Sigma}+)(v=1). At 57, 110, 200, 357, and 490 cm{sup -1} above this product threshold, vibrational branching ratios for the singlet products were measured and compared to phase space theory (PST), separate statistical ensembles (SSE), and variational RRKM (var. RRKM).
Date: December 1, 1996
Creator: Wade, E.A.
Partner: UNT Libraries Government Documents Department

The effects of pseudo magnetic fields in molecular spectra and scattering

Description: Pseudo magnetic fields appear in the Born-Oppenheimer method for molecules when conical intersections or electronic angular momenta are taken into account. These fields are not real magnetic fields but they have the same mathematical properties and can lead to real observable effects in the dynamics of molecules. A general vector potential (gauge theory) approach for including these field effects in the Born-Oppenheimer method is introduced and applied to H + O{sub 2} scattering and the vibrational spectrum of Na{sub 3}(X) for zero total angular momentum (J = 0). The scattering results for HO{sub 2} show significant shifts in the resonance energies and lifetimes due to a magnetic solenoid type field originating from the C{sub 2v} conical intersection in HO{sub 2}. Significant changes in the state-to-state transition probabilities are also observed. The non-degenerate A{sub 1} and A{sub 2} vibrational spectra of Na{sub 3}(X) show significant shifts in the energy levels due to a magnetic solenoid type field originating from the D{sub 3h} conical intersection in Na{sub 3}. These two examples show that the effects of pseudo magnetic fields can be significant and in many cases they must be included in order to obtain agreement between theory and experiment. The newly developed gauge theory techniques for treating pseudo magnetic fields are also relevant for including the effects of real magnetic fields.
Date: December 31, 1996
Creator: Kendrick, B.
Partner: UNT Libraries Government Documents Department

Infrared spectroscopy of nonclassical ions and their complexes

Description: This thesis describes an infrared spectroscopic study on the structures and dynamics of the nonclassical ions and their complexes, using ion trap vibrational predissociation spectroscopy. Chapter One provides an introduction to the experimental apparatus used in this work. Chapter Two describes the previous theoretical and experimental works on the carbonium ion CH{sub 5}{sup +} and infrared spectroscopic and theoretical works on CH{sub 5}{sup +}. CH{sub 5}{sup +} was predicted to scramble constantly without possessing a stable structure. In Chapter Three, the infrared spectroscopy for the molecular hydrogen solvated carbonium ions CH{sub 5}{sup +}(H{sub 2}){sub n} (n=1-6) in the frequency region of 2700-4200 cm{sup {minus}1} are presented and compared with the results of ab initio molecular dynamics simulation on CH{sub 5}{sup +}(H{sub 2}){sub n} (n=0-3). The results suggested that the scrambling of CH{sub 5}{sup +} slowed down considerably by the stabilization effects of the solvent H{sub 2} molecules, and it was completely frozen out when the first three H{sub 2} molecules were bound to the core CH{sub 5}{sup +}. Chapter Four presents the complete infrared spectra for the solvated carbonium ions, CH{sub 5}{sup +}(A){sub x}(B){sub y} (A,B=H{sub 2}, Ar, N{sub 2}, CH{sub 4};x,y=0-5) in the frequency region of 2500-3200 cm{sup {minus}1}. As the binding affinities of the solvent molecules and the number of the solvent molecules in the clusters increased, the scrambling of CH{sub 5}{sup +} slowed down substantially. The structures of the solvated carbonium ions and the evidence for rapid proton transfer in CH{sub 5}{sup +}(CH{sub 4}) were also presented. Chapter Five presents the vib-rotational spectrum for the H-H stretching mode of the silanium ion SiH{sub 5}{sup +}. The results suggested that SiH{sub 5}{sup +} can be described as a complex of SiH{sub 3}{sup +} and a freely internally rotating H{sub 2}, analogous to, but distinct from CH{sub 5}{sup +}.
Date: January 1, 1995
Creator: Boo, D.W.
Partner: UNT Libraries Government Documents Department

Symbolic derivation of high-order Rayleigh-Schroedinger perturbation energies using computer algebra: Application to vibrational-rotational analysis of diatomic molecules

Description: Rayleigh-Schroedinger perturbation theory is an effective and popular tool for describing low-lying vibrational and rotational states of molecules. This method, in conjunction with ab initio techniques for computation of electronic potential energy surfaces, can be used to calculate first-principles molecular vibrational-rotational energies to successive orders of approximation. Because of mathematical complexities, however, such perturbation calculations are rarely extended beyond the second order of approximation, although recent work by Herbert has provided a formula for the nth-order energy correction. This report extends that work and furnishes the remaining theoretical details (including a general formula for the Rayleigh-Schroedinger expansion coefficients) necessary for calculation of energy corrections to arbitrary order. The commercial computer algebra software Mathematica is employed to perform the prohibitively tedious symbolic manipulations necessary for derivation of generalized energy formulae in terms of universal constants, molecular constants, and quantum numbers. As a pedagogical example, a Hamiltonian operator tailored specifically to diatomic molecules is derived, and the perturbation formulae obtained from this Hamiltonian are evaluated for a number of such molecules. This work provides a foundation for future analyses of polyatomic molecules, since it demonstrates that arbitrary-order perturbation theory can successfully be applied with the aid of commercially available computer algebra software.
Date: July 1, 1997
Creator: Herbert, J.M.
Partner: UNT Libraries Government Documents Department

Spectroscopic investigation of the vibrational quasi-continuum arising from internal rotation of a methyl group. Final report, 1990 - 1993

Description: Spectroscopy was used to study the vibrational quasi-continuum arising from internal rotation of the methyl group in acetaldehyde. We now understand the torsion-rotation levels from all 3 torsional states below the top of the torsional barrier. Investigations of four ordinary vibrational states in acetaldehyde are in progress.
Date: December 31, 1993
Creator: Hougen, J.T.
Partner: UNT Libraries Government Documents Department

A scaling theory for the assignment of spectra in the irregular region. Continuation progress report

Description: The ultimate object of our program is to learn how to extract information about molecular rovibrational motions from experimental spectra or calculated energy levels. This goal of spectroscopy and theoretical chemistry has historically only been possible in the regular spectral region. Our project is one of several which are aimed at spectral interpretation in the chaotic or mixed chaotic plus regular regions. Our particular tools involve a scaling theory developed under our previous DOE support period. This theory uses experimentally fitted spectral Hamiltonians or Hamiltonian`s whose potentials are calculated using quantum chemistry, to obtain energy levels as a function of h{sup -1}. The scaling theory then uses this input to highlight the actions of the subset of all periodic orbits which control the dynamics at any given energy up to dissociation. The periodic orbits themselves, are the skeleton of classical phase space for the molecular motions and are found by classical non-linear dynamic techniques. The finding and following of these periodic orbits by constructing a bifurcation diagram, and in 2D, Poincare surfaces of section, is labor intensive and takes much of our available man hours. We have two projects, {open_quotes}acetylene{close_quotes} and {open_quotes}NO{sub 2}.{close_quotes} Below we first briefly sketch the results of the classical phase space study using the fitted spectral Hamiltonian that describes pure bending dynamics of in the acetylene X{sup 1}{Sigma}{sub g}{sup +} state to 15,000 cm{sup -1} of internal energy. The work on NO{sub 2} will follow. The specific purpose of this part of our work is to establish relations between experimental data and quantum mechanical results on one side and the behaviour of the dynamics given by the corresponding classical Hamiltonian function on the other side for the bend vibrations of the C{sub 2}H{sub 2} molecule. We transform it into a classical Hamiltonian function given in action ...
Date: June 1, 1998
Creator: Taylor, H.S.
Partner: UNT Libraries Government Documents Department

Resonant multiphoton ionization spectra of molecules and molecular fragments. Technical progress report

Description: objectives of this research are the development and application of theoretical techniques for studying several resonant multiphoton ionization processes in molecules. Specific problems of interest pertain to experimental studies of such spectra in which the photoelectron energy and angular distributions are determined.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Catalytic applications of mono- and dinuclear complexes containing metal-carbon sigma bonds. Final report, November 1, 1993--October 31, 1996

Description: This report discusses results from several studies involved in the project. Investigations include: vibrational models for surface olefins and alkylidenes; mechanism of the formation and fragmentation of diosmacyclobutanes; reaction of dienes and allenes with diosmacyclobutanes; determination by nematic phase NMR of the structure of mononuclear and dinuclear ethylene complexes of osmium; and generation of ``coordinatively unsaturated`` complexes by protonation of methyl osmium complexes.
Date: December 31, 1996
Creator: Norton, J.R.
Partner: UNT Libraries Government Documents Department

Inelastic neutron scattering study of the (O{sub 4}H{sub 4}) substitution in garnet

Description: Inelastic scattering data have been collected at incident neutron energies of 50, 150, 300 and 600 meV for hydrogarnet [Sr{sub 3}Al{sub 2}(O{sub 4}H{sub 4}){sub 3}], a model compound for silicate hydrogarents found in the Earth`s crust and mantle. The vibrational spectrum is characterized by a relatively sharp O-H stretch at {approximately}460 meV, which is consistent with the weak O...H bond ({approximately}2.65 {angstrom}) and other complex features in the 20-100 meV region. The mode assignment for isostructural grosslar and the infrared spectra for hydrogarnet were used as a basis for the intreperation of many of the neutron spectral features.
Date: July 14, 1997
Creator: Lager, G.A.; Nipko, J.C. & Loong, C.K.
Partner: UNT Libraries Government Documents Department

The phonon density of states measured with synchrotron radiation and nuclear resonances.

Description: In this experiment, we will use synchrotron radiation to measure the density of states of vibrational excitations (phonons.) Each group of students will conduct an experiment at sector 3-ID of the Advanced Photon Source, the nation's premier synchrotron radiation facility. We provide one support staff per group, i.e., Drs. Michael Hu, Sarvjit Shastri, Wolfgang Sturhahn, and Tom Toellner will help their group to perform the experiment and interpret the data. After data collection (1-2 h per group), the remaining time will be spent with evaluation and interpretation. In addition to your own data, we provide similar sets of data. Computer hardware (iMac running as X-terminals) and software for data manipulation will be provided. It is important that you understand the basic principles of the experimental method. Therefore we strongly recommend that you read the next section and the attached article Phonon Density of States Measured by Inelastic Nuclear Resonant Scattering. You are expected to use this description to familiarize yourself with the experimental setup and its individual components before the start of the experiment. You should be able to solve at least 75% of the quiz correctly. If you have particular questions or a general problem in understanding this document, please contact Dr. W. Sturhahn, Bldg. 431, Rm. D007, tel. 0163.
Date: January 26, 2001
Creator: Sturhahn, W.; Hu, M.; Shastri, S. & Toellner, T.
Partner: UNT Libraries Government Documents Department

Non-thermal photodesorption of N{sub 2} from Ag(111)

Description: The authors have measured translational and rotational energy distributions of N{sub 2} molecules following desorption from a Ag(111) surface by infrared (1,064 nm) radiation. The observed desorption yields were large even at laser fluences far below that required for laser induced thermal desorption. State resolved laser techniques using coherent VUV radiation showed that the rotational and translational energy distributions of the desorbing N{sub 2} molecules are not consistent with the predictions of the heat diffusion model governing laser induced surface heating. These results suggest that physisorbed adsorbates can couple directly to the nascent phonon distribution or the nascent electron-hole pairs in the photoexcited substrate without heating of the surface.
Date: February 1998
Creator: Rao, R. M.; Beuhler, R. J. & White, M. G.
Partner: UNT Libraries Government Documents Department

Resonance enhanced multiphoton and single-photon ionization of molecules and molecular fragments. Annual technical report, May 1, 1994--April 30, 1995

Description: In resonance enhanced multiphoton ionization (REMPI) pulsed laser radiation is utilized to prepare a molecule in an excited state via absorption of one or more photons and to subsequently ionize that level before it decays. A remarkable feature of REMPI is that the very narrow bandwidth of laser radiation makes is possible to select a specific rotational level in the initial (ground) state and to prepare the excited state of interest in a single rotational level. By suitable choice of the excitation step, it is thus possible to selectively ionize a species of interest present in very minor concentrations without ionizing any other species that may be present. This feature makes REMPI a very powerful tool for ultrasensitive detection of trace or transient species.
Date: July 1, 1997
Creator: McKoy, V.
Partner: UNT Libraries Government Documents Department