The room-temperature nonlinear absorption spectra of a GaInAs/AlInAs and a GaAlInAs/AlInAs multiple quantum well (MQW) were measured near 1.3 μm using a pump-probe technique. Saturation carrier densities at the heavy-hole exciton peak were determined to be 1.2 x 10¹⁸ and 1.0 x 10¹⁸ cm⁻³ with carrier lifetimes of ≃ 2.3 ns and ≃ 750 ps for the two samples, respectively. Fabry-Perot etalons with integrated mirrors grown by molecular beam epitaxy (MBE) with GaInAs/AlInAs MQWs as spacer layers were also fabricated as optical switching devices. A 175 ps recovery time was measured for the etalon at room temperature.

A new high resolution Fourier transform interferometer has been constructed for the study of infrared molecular spectra. The instrument is capable of producing high quality spectra with an unapodized resolution of.004 cm$\sp{-1}$ for the wavenumber range 2000 to 10000 cm$\sp{-1}$. Described here are the details of construction and operating procedures for this instrument as well as the data collection, control and analysis software written specifically for it. / The new FTS instrument has been used to measure the torsion-rotation absorption spectrum of the O-H stretch vibration in gaseous hydrogen peroxide. Over 3000 line assignments have been made, including many arising from torsional "hot band" transitions. Many new assignments have been made for the weak n = 0$\to$1 bands and assignments for the very weak n = 1$\to$2 bands are reported for the first time. These new data have been used to determine the torsion-rotation energy levels and inertial constants for each of the five lowest torsion states of the excited antisymmetric O-H stretch. The shape of the potential curve was estimated from these using a semi-rigid rotor model; the limitations of the model are examined. / Source: Dissertation Abstracts International, Volume: 53-07, Section: B, page: 3554. / Major Professor: Robert H. Hunt. / Thesis (Ph.D.)--The Florida State University, 1992.

Three comparative fluorescence emissions are shown to be observable from a common initial excited singlet state in a prototype aminosalicylate molecule: p-NR$\sb2$C$\sb6$H$\sb3$(OR$\sp\prime$)COOR$\sp{\prime\prime}$, PDASE (R = CH$\sb3$, R$\sp\prime$ = H and R$\sp{\prime\prime}$ = CH$\sb3$). All molecular structures are with the (OR$\sp\prime$) group ortho to the COOR$\sp{\prime\prime}$ group. The steady-state fluorescences are assigned as the normal fluorescence ${\rm S\sb1(\pi,\pi\sp\*) \to S\sb0}$, the twisted intramolecular charge-transfer or TICT-state fluorescence S$\sbsp{1}{\prime\prime}$(TICT) $\to$ S$\sb0$, and the intramolecular proton-transfer fluorescence S$\sbsp{1}{\prime}$(PT) $\to$ S$\sbsp{0}{\prime}$. Two excited state absorptions are also believed to be present for PDASE. The excited-state absorptions are assigned as the absorption from the first excited TICT singlet S$\sbsp{n}{\prime\prime}$(TICT) $\gets$ S$\sbsp{1}{\prime\prime}$(TICT), and the absorption from the first excited state of the proton-transfer tautomer S$\sbsp{n}{\prime}$(PT) $\gets$ S$\sbsp{1}{\prime}$(PT). / Several compounds were designed and synthesized to isolate the emission-type that was of interest. Among these were MABAE (R = H, R$\sp\prime$ = CH$\sb3$ and R$\sp{\prime\prime}$ = CH$\sb3$) which isolates for normal emission processes; PASE (R = H, R$\sp\prime$ = H and R$\sp{\prime\prime}$ = CH$\sb3$) which isolates for proton-transfer processes in the shifted or F$\sb2$ band; and, MDABAE (R = CH$\sb3$, R$\sp\prime$ = CH$\sb3$ and R$\sp{\prime\prime}$ = CH$\sb3$) which isolates for TICT processes in the F$\sb2$ band. Using steady-state absorption and emission, the relative shift in fluorescence wavelength maxima vs. the solvent polarity index E$\sb{\rm T}$, picosecond optical multichannel analyzer resolved transient absorption, and picosecond streak camera resolved fluorescence dynamics the assignments for the studied molecular systems were corroborated. / Source: Dissertation Abstracts International, Volume: 50-05, Section: B, page: 1959. / Major Professor: Michael Kasha. / Thesis (Ph.D.)--The Florida State University, 1989.

Calculations have been carried out in the distorted-wave Born approximation for electron-impact excitation of the individual 2p fine-structure states of the hydrogen atom. Results are given for 54.4, 100, and 200 eV. The purpose was not to improve on existing more elaborate calculations of the state multipoles of the excited 2p states, but rather to investigate spin-related phenomena, such as an incident polarized beam, polarized target atoms, and the polarization of the scattered electrons when unpolarized electrons are incident on unpolarized target atoms. The bound state wave functions are constructed using the total angular momentum scheme, $\vert JM\sb{J}\rangle = \sum\limits\sb{M\sb{L}M\sb{S}}C(LSJ;M\sb{L}M\sb{S}M\sb{J})\vert LM\sb{L}SM\sb{S}\rangle$, and the Percival-Seaton hypothesis is not used. We then construct explicitly-spin-dependent scattering amplitudes. This approach is to be contrasted with previous calculations which use $\vert LM\sb{L}SM\sb{S}\rangle$ wave functions and assume that the sum of the electron spin projections is conserved in the collision, or with calculations which use uncoupled wave functions. / The spin polarization of the scattered electrons resulting from scattering unpolarized electrons on unpolarized ground state hydrogen atoms (the 'fine-structure effect') is found to result here from interference of the direct and exchange scattering amplitudes. Distortion of the scattered waves by the atomic potential produces a nonzero component of the transferred angular momentum perpendicular to the scattering plane. This orbital angular momentum orientation of the excited atom is then transferred to the scattered electron via angular momentum algebra. The spin-orbit interaction in the excited atom is the origin of the spin polarization, since it produces a sufficient energy separation of the fine structure states to allow them to be studied separately. / Source: Dissertation Abstracts International, Volume: 56-04, Section: B, page: 2085. / Major Professor: W. N. Shelton. / Thesis (Ph.D.)--The Florida State University, 1995.

The framework of density functional theory is used to define rigorously quantities of general chemical interest and investigate their properties. The computational schemes for calculating their values are based on the topological theory of atoms in molecules. General and spin-specific atomic Fukui indices are defined and calculated for six model molecular systems. The ROHF level of theory is estimated as the least expensive method for their evaluation which produces reliable results. A scheme for energy decomposition of molecular interactions, which is applicable to any level of electronic structure theory, is proposed. The scheme partitions the interaction energy into classical electrostatic, charge-transfer, and wave function relaxation components, which are true observables converging smoothly with increasing basis sets. Results of several test calculations are compared with those produced by other energy partitioning schemes and found to exhibit superior numerical stability. The atomic softness matrix, which is a generalization of the Huckel atom-atom polarizability matrix, is defined and used in a rigorous reformulation of the electronegativity equalization methods. A computational scheme for its evaluation is proposed and illustrated with several numerical examples. The charge distribution in substituted polyynes is investigated with the new formalism. Individual spin contributions to charge transfer in molecules are analysed. The intra- and interspin components of the bond hardness tensor are rigorously defined. Stability conditions with respect to charge transfer and spin polarization are formulated for closed-shell systems. The energetics of electron flow is illustrated using model systems. Some non-specific electrostatic effects of solvation in polar molecular systems are studied using a simple continuum-type model. The analysis of these effects / in terms of electronegativity equalization and charge transfer show that, based on the electrostatics of their solvation, most systems fall into two categories according to the solvation induced molecular geometry change. / Source: Dissertation Abstracts International, Volume: 56-06, Section: B, page: 3216. / Major Professor: Jerzy Cioslowski. / Thesis (Ph.D.)--The Florida State University, 1995.

The matrix metalloproteinases (MMPs) are a family of zinc proteinases that is collectively capable of degrading the major components of the extracellular matrix. A variety of synthetic peptides has been prepared which are models for the human MMP and their substrates to study structure-function relationships in this enzyme-substrate system. To elucidate the sequence specificity of the MMP, the k$\rm\sb{cat}/K\sb M$ values for the hydrolysis of over 50 synthetic octapeptides has been investigated. Similarities, as well as distinct differences have been found between the individual MMP with the largest differences occurring at subsites P$\rm\sb1, P\sb1\sp\prime$ and P$\sb3\sp\prime.$ Based on these data, quenched-fluorescence substrates with optimized sequences have been developed for five human MMP. The key features of these heptapeptides are a tryptophan on the P$\rm\sb n\sp\prime$ side and a dinitrophenol quenching group on the amino terminus. To assess the role of the triple helical conformation in the collagenase-collagen system, a series of triple helical peptides has been prepared and shown to compete with collagen in collagenase assays. This provides evidence for the existence of a triple helical recognition site distinct from the active site. All of the MMP are secreted as zymogens and it has been postulated that the portion of the propeptide surrounding a critical cysteine is responsible for maintaining latency. Conformational energy calculations and mutagenesis studies have suggested that this region adopts a specific conformation that stabilizes the latent form. Peptide models of this region of the propeptide have been prepared and shown to inhibit the MMP. CD and NMR studies, however, have failed to provide evidence for the predicted peptide conformation. Thus, the observed inhibition may reflect their propensity to adopt the propeptide conformation upon binding to the enzyme. / Source: Dissertation Abstracts International, Volume: 56-01, Section: B, page: 0222. / Major Professor: Harold E. Van Wart. / Thesis (Ph.D.)--The Florida State University, 1994.

No description available.

We present high accuracy calculations of molecular systems in a basis of explicitly correlated gaussian functions. Included in the work is the derivation of integrals over the static electric field Born-Oppenheimer and non-Born-Oppenheimer Hamiltonians in this basis. Also, we present the first derivation and implementation of analytical gradients of the total molecular energy with respect to variational parameters in the basis functions. The program written based on these formulae has been implemented in FORTRAN 90 and MPI to run on large parallel systems. We have performed the first calculations of non-linear optical properties of molecules without the Born-Oppenheimer approximation for systems with more than 1 electron, including isotopomers of LiH and H2. The results agree well with experiment.

The pairing of fermionic particles is an essential ingredient of superconductivity and of the superfluidity of 3He. While such phenomena are accurately described by BCS theory in the limit of weak pairing strength, a complete understanding remains elusive when pairing strength is increased, such as in high temperature superconductors. We create ultracold gases of trapped fermionic 6Li atoms, through which we directly observe fermionic pairing. In our system, there are no impurities whatsoever, and parameters such as the number and temperature of the trapped atoms are precisely and independently controlled. In addition, a Feshbach resonance enables the continuous tuning of interaction strength and sign between the paired atoms. This control allows us to observe the smooth crossover of a molecular Bose Einstein condensate (MBEC) to a superfluid of weakly interacting Cooper pairs. With these tools, we have performed several fundamental measurements of pairing in fermionic systems. We use optical molecular spectroscopy to precisely measure the closed-channel contribution to the many body state of paired 6Li atoms within a broad Feshbach resonance. The magnitude of this contribution is small, and supports the concept of universality for the description of broad Feshbach resonances. Moreover, the dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and for the first time, into the weakly interacting BCS regime. We also prepare a polarized Fermi gas with unequal numbers of two spin states of 6Li atoms. The real-space densities of the polarized, strongly-interacting, two-component Fermi gas reveal two low temperature regimes. At the lowest temperatures, the gas separates into a phase with a uniformly paired superfluid core surrounded by a shell of normal, unpaired atoms. This phase separation is accompanied by a spatial deformation of the core. At higher temperatures, the uniformly paired core persists, though it does not deform. This temperature dependence is consistent with a tri-critical point in the phase diagram. These measurements of pairing in a polarized Fermi gas are relevant to predictions of exotic phases of quark matter and magnetized superconductors.

The nature of molecular vibrational coordinates is elucidated through the use of canonical coordinate transformations of the Hamiltonian. The importance of studying molecular vibrations with quantum mechanical calculational techniques is discussed and the methods for doing these calculations in rectilinear rotations of the bond coordinates are presented. Chief among these methods are prediagonalization and the transformation method, also known as the discrete variable representation. The results of coordinate rotation calculations on a three-coordinate stretching-only model of acetylene are presented and discussed. The results of calculations on two two-coordinate subsystems of acetylene are also presented. In all of these cases prediagonalization and rotated coordinates result in a substantial improvement in the quality of the zero order basis as measured by the projection of the eigenstate of interest onto the product function basis state with the same quantum numbers. Optimized coordinate rotation calculations for a two-coordinate stretching-only model of hydrogen cyanide are presented. The results are similar to those of the acetylene calculations. The physical interpretation of the hydrogen cyanide calculations is easier because contour plots of the entire system are possible. An unexpected and previously unexplained intensity pattern in the hydrogen cyanide vibrational overtone spectrum is analyzed and clarified. Finally, drawbacks to these calculational techniques are discussed and possible improvements and future uses are suggested.