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Extended Hueckel $beta$ parameters applied to diatomic molecules

Description: From international symposium on atomic, molecular, solidstate theory, and quantum statistics; Sanibel lsland, Florida, USA (20 Jan 1974). Atom-atom separations predicted by extended Huckel theory using four BETA parameter approximations are compared for 15 diatomic molecules. Equilibrium separations R/ sub e/ determined from a new proposed formula for the BETA parameter are compared with R/sub e/'s resulting from the Mulliken-Wolfsberg-Helmholtz, Cusachs, and Jug BETA formulas. Results show that the new BETA formula is best in its prediction of R/sub e/'s. The new formula has the required property of yielding rotationally invariant results. (auth)
Date: January 1, 1974
Creator: Engelke, S.Z.
Partner: UNT Libraries Government Documents Department

Sheared Rotation Effects on Kinetic Stability in Enhanced Confinement Tokamak Plasmas, and Nonlinear Dynamics of Fluctuations and Flows in Axisymmetric Plasmas

Description: Sheared rotation dynamics are widely believed to have significant influence on experimentally observed confinement transitions in advanced operating modes in major tokamak experiments, such as the Tokamak Fusion Test Reactor (TFTR) with reversed magnetic shear regions in the plasma interior. The high-n toroidal drift modes destabilized by the combined effects of ion temperature gradients and trapped particles in toroidal geometry can be strongly affected by radially sheared toroidal and poloidal plasma rotation. In previous work with the FULL linear microinstability code, a simplified rotation model including only toroidal rotation was employed, and results were obtained. Here, a more complete rotation model, that includes contributions from toroidal and poloidal rotation and the ion pressure gradient to the total radial electric field, is used for a proper self-consistent treatment of this key problem. Relevant advanced operating mode cases for TFTR are presented. In addition, the complementary problem of the dynamics of fluctuation-driven E x B flow is investigated by an integrated program of gyrokinetic simulation in annulus geometry and gyrofluid simulation in flux tube geometry.
Date: December 1, 1997
Creator: Rewoldt, G.; Beer, M.A.; Chance, M.S.; Hahm, T.S.; Lin, Z. & Tang, W.M.
Partner: UNT Libraries Government Documents Department

Coulomb excitation of the 242mAm isomer

Description: The {sup 242m}Am isomer, a well-known candidate for photo-depopulation research, has been studied in this first ever Coulomb excitation of a nearly pure ({approx} 98%) isomer target. Thirty new states, including a new rotational band built on a K{sup {pi}} = 6{sup -} state have been identified. Strong K-mixing results in nearly equal populations of the K{sup {pi}} = 5{sup -} and 6{sup -} states. Newly identified states have been assigned to the K{sup {pi}} = 3{sup -} rotational band, the lowest states of which are known to decay into the ground-state band. Implications regarding K-mixing and Coulomb excitation paths to the ground state are discussed.
Date: October 24, 2006
Creator: Hayes, A; Cline, D; Moody, K; Wu, C; Becker, J; Carpenter, M et al.
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

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

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

{Delta}I = 4 bifurcation: Origins and criteria

Description: The new {gamma}-ray detector arrays have demonstrated that rotational sequences in certain superdeformed bands with angular momentum differing by two can split into two branches. This is commonly called {Delta}I = 4 bifurcation, and has attracted considerable interest in the nuclear structure community. An alternative approach for the {Delta}I = 4 bifurcation phenomenon has been presented without introducing either a Y{sub 44} deformation or an I{sup 4} term in the Hamiltonian explicitly. The optimal criteria for observing the phenomenon have been discussed as well.
Date: December 31, 1995
Creator: Zhang, J.Y.; Sun, Y. & Guidry, M.
Partner: UNT Libraries Government Documents Department

Very extended shapes in the A~;110 region

Description: High-angular-momentum states in {sup 108}Cd were populated via the {sup 64}Ni({sup 48}Ca,4n) reaction at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. A rotational band has been observed with a dynamic moment of inertia and deduced lower limit of the quadrupole moment suggesting a major-to-minor axis ratio larger than 1.8:1, placing it among the most deformed structures identified in any nucleus, to date.
Date: September 12, 2001
Creator: Clark, R.M.; Fallon, P.; Gorgen, A.; Cromaz, M.; Deleplanque,M.A.; Diamond, R.M. et al.
Partner: UNT Libraries Government Documents Department

Very extended shapes in 108Cd: evidence for the occupation of 'hyper-intruder' orbitals

Description: High-spin states in {sup 108}Cd were studied following the reaction {sup 64} Ni({sup 48}Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structures e.g. in the A {approx} 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the {pi}i{sub 13/2}hyper-intruder orbital is occupied in these newly observed bands.
Date: July 1, 2002
Creator: Gorgen, A.; Clark, R.M.; Fallon, P.; Cromaz, M.; Deleplanque, M.A.; Diamond, R.M. et al.
Partner: UNT Libraries Government Documents Department

The N=90 transitional nuclei {sup 150}Nd and {sup 152}Sm revisited

Description: The purpose of this paper is to show that recent data on the ground-state band and excited states based on the 0{sub 2}{sup +} level in {sup 15}Nd and {sup 152}Sm, especially the measured B(E2) values, can be well described by including a {Delta}K = 0 coupling between rotational bands. This is contrary to recent statements in the literature. The experimental data are compared with models which have supported the widely differing interpretations of these transitional nuclei. These interpretations include describing excited states as rotational excitations of single-phonon states, the multiphonon ''phase coexistence'' picture, and the X(5) critical-point description.
Date: January 21, 2003
Creator: Clark, R.M.; Cromaz, M.; M.A., Deleplanque; Diamond, R.M.; Fallon, P.; Gorgen, A. et al.
Partner: UNT Libraries Government Documents Department

Isotope, Electric Field, and Vibrational State Dependence of Single Rotational Level Lifetimes of S1 Formaldehyde

Description: Additional single rovibronic level lifetimes of S{sub 1} H{sub 2}CO and D{sub 2}CO have been measured under collisionless conditions. The H{sub 2}CO 4{sup 1} lifetimes vary at least a factor of 150, from 20 nsec to 3.10 {micro}sec. The observed D{sub 2}CO 4{sup 1} lifetimes fluctuate about {+-} 20% around a mean value of 6.2 {micro}sec, which is probably close to the pure radiative lifetime. In contrast, the observed D{sub 2}CO 4{sup 3} lifetimes vary from 1.09 to 2.46 {micro}sec and the 2{sup 1} 4{sup 3} lifetimes vary from 212 nsec to 1.61 {micro}sec. The onset of rotational state lifetime fluctuations in D{sub 2}CO thus coincides with the high pressure D{sub 2} + CO photochemical threshold. All of these results are explained in terms of a collisionless sequential decay mechanism, S{sub 1} {yields} S{sub 0} {yields} H{sub 2}(D{sub 2}) + CO. The last step probably involves tunneling through a barrier for the lower energies studied. For several H{sub 2}CO 4{sup 1} rotational levels application of a uniform external electric field of 0-4.6 kV/cm can change the fluorescence lifetime by at least a factor of 4. This result is understood in terms of small ({approx}< 0.05 cm{sup -1}) shifts in S{sub 1}-S{sub 0} energy spacings. Quantitative estimates of S{sub 1}-S{sub 0} intramolecular couplings, S{sub 0} widths due to dissociation, and S{sub 0} level spacings are derived in favorable cases.
Date: December 1, 1979
Creator: Weisshaar, James C. & Moore, C. Bradley
Partner: UNT Libraries Government Documents Department

GAMMASPHERE+FMA : a journey beyond the proton drip-line.

Description: The majority of experiments performed during the 2-year long stay of GAMMAS-PHERE at the Argonne National Laboratory aimed to study proton-rich nuclei far from the line of stability at and beyond the proton drip-line. A high reaction channel selectivity was required to assign in-beam {gamma}-ray transitions to weakly populated exotic nuclei in the presence of background from strong reaction channels. In many of the experiments this was achieved by using the Argonne fragment mass analyzer to separate heavy-ion fusion-evaporation reaction products from scattered beam and disperse them according to their mass-over-charge-state ratio. For medium mass and heavy a and proton emitters the Recoil-Decay Tagging method was implemented. In-beam {gamma}-ray transitions were observed in several proton emitters between Z=50 and Z=82. Among others, rotational bands were assigned to {sup 141}Ho and {sup 131}Eu. A quadruple deformation of {beta}=0.25(4) was deduced for the ground state in {sup 141}Ho from the extracted dynamic moment of inertia. Based on observed band crossings and signature splittings the 7/2{sup {minus}} [523] and 1/2{sup +}[411] configurations were proposed for the ground state and the isomeric state, respectively. Comparison with particle-rotor calculations indicates, however, that {sup 141}Ho may have significant hexadecapole deformation and could be triaxial.
Date: November 30, 2000
Creator: Seweryniak, D.; Woods, P. J.; Ressler, J. J.; Davids, C. N.; Heinz, A.; Sonzogni, A. A. et al.
Partner: UNT Libraries Government Documents Department

Femtosecond Raman induced polarization spectroscopy studies of coherent rotational dynamics in molecular fluids

Description: We develop a polarization-sensitive femtosecond pump probe technique, Raman induced polarization spectroscopy (RIPS), to study coherent rotation in molecular fluids. By observing the collisional dephasing of the coherently prepared rotational states, we are able to extract information concerning the effects of molecular interactions on the rotational motion. The technique is quite sensitive because of the zero background detection method, and is also versatile due to its nonresonant nature.
Date: May 1, 1997
Creator: Morgen, M.M.
Partner: UNT Libraries Government Documents Department

In-beam studies of proton emitters using the Recoil-Decay Tagging method

Description: The last five years have witnessed a rapid increase in the volume of data on proton decaying nuclei. The path was led by decay studies with recoil mass separators equipped with double-sided Si strip detectors. The properties of many proton-decaying states were deduced, which triggered renewed theoretical interest in the process of proton decay. The decay experiments were closely followed by in-beam {gamma}-ray studies which extended one's knowledge of high-spin states of proton emitters. The unparalleled selectivity of the Recoil-Decay Tagging method combined with the high efficiency of large arrays of Ge detectors allowed, despite small cross sections and overwhelming background from strong reaction channels, the observation of excited states in several proton emitters. Recently, in-beam studies of the deformed proton emitters {sup 141}Ho and {sup 131}Eu have been performed with the GAMMASPHERE array of Ge detectors and the Fragment Mass Analyzer at ATLAS. Evidence was found for rotational bands in {sup 141}Ho and {sup 131}Eu. The deformations and the single-particle configurations proposed for the proton emitting states from the earlier proton-decay studies were confronted with the assignments deduced based on the in-beam data. It should be noted that the cross section for populating {sup 131}Eu is only about 50 nb, and it represents the weakest channel ever studied in an in-beam experiment.
Date: January 19, 2000
Creator: Seweryniak, D.; Woods, P. J.; Ressler, J.; Davids, C. N.; Heinz, A.; Sonzogni, A. et al.
Partner: UNT Libraries Government Documents Department

Energy randomisation. How much of rotational phase space is explored? How long does it take?

Description: In applying modern theories (RRKM) of unimolecular reaction, it is necessary to decide the volume of phase space in which the energy is assumed to be randomized. The question of whether the K rotational quantum number is conserved impacts on that choice. The conceptual sequence from experimental spectra, through analysis, and interpretation in terms of K relaxation is described for ethanol and 1-butyne in the 3 micron region. The interpretation of molecular eigenstate spectra involves identification of the bright state from the coherent excitation of part of the spectrum, evaluation of the rate of energy transfer out of the bright state, deducing the mechanism of the coupling of the bright state to the bath states, and modeling the spectra in order to determine the average coupling parameters for anharmonic coupling and Coriolis interactions.
Date: December 1995
Creator: Perry, D. S.; Bethardy, G. A.; Davis, M. J. & Go, J.
Partner: UNT Libraries Government Documents Department

Superdeformation in the A=150 and A=190 regions.

Description: Superdeformation has been established for over a decade in the mass 150 region and nearly as long in the A=190 region. The first measurements directed at nuclei in these regions concentrated on mapping out the superdeformed (SD) islands by identifying SD rotational bands in {gamma}-ray coincidence data. These early studies provided new insights into the physics of superdeformation, but also raised unexpected issues. The new gamma-ray arrays (Gammasphere, Eurogam/Euroball and Gasp) have provided a wealth of new data on properties of SD states in these two mass regions. This paper highlights some of the more recent results from the large arrays which have addressed the outstanding issues in the field, namely, {Delta}I = 4 staggering, identical bands, SD vibrational bands, and questions about the feeding into and the decay out of the SD well.
Date: December 1, 1998
Creator: Carpenter, M. P.
Partner: UNT Libraries Government Documents Department

Possible triaxial superdeformation in {sup 174}Hf.

Description: Three, possibly four, regularly spaced rotational bands with large dynamical moments of inertia, which are consistent with known superdeformed bands in the Lu/Hf region, have been identified in {sup 174}Hf. The states were populated in the {sup 130}Te({sup 48}Ca,4n) reaction at a beam energy of 194 MeV. The Gammasphere array detected the emitted gamma radiation. Ultimate cranker calculations predict substantial triaxial deformation ({gamma} {approx} {+-} 17{sup o}) for highly deformed {sup 174}Hf structures. However, {sup 174}Hf is eight neutrons away from the previously established N = 94 triaxial superdeformed shell gap. Shell gaps at N = 100 and 106 with {gamma} {ge} 15{sup o} are observed when {var_epsilon}{sub 2} {approx} 0.45, which may be responsible for the predicted TSD minima in {sup 174}Hf.
Date: September 18, 2002
Creator: Hartley, D. J.; Djongolov, M.; Riedinger, L. L.; Kondev, F. G.; Janssens, R. V. F.; Abu Saleem, K. et al.
Partner: UNT Libraries Government Documents Department