Thesis--Ph. D., University of Hong Kong, 1987.

A binary mixture of copper (II) chloride and gold (III) chloride solutions were introduced into a FT-ICR Mass Spectrometer through electrospray ionization techniques to produce ion clusters in the gaseous state. A series of families of ion clusters were detected across a range of different concentrations and they were identified as heterometallic mono-cationic clusters with possible hydrated and ligated species present as well. Ab initio calculations on the first member of the family of hetero-metallic monocationic species detected in the mass spectra were carried out using density function theory (DFT) methods and correlation consistent (cc) basis sets. Equilibrium bond lengths and vibrational frequencies were computed and resulting values compared with published literature values. / published_or_final_version / Applied Geosciences / Master / Master of Science

This research focuses on developing selective FRET peptidyl metal ion sensors as a portable and less costly alterative to traditional atomic spectrometric techniques. Initially, a selective sensor for Cu²⁺ was developed that consisted of glycine and aspartic acid residues and the FRET pair tryptophan (donor) and dansyl (acceptor). Aspartic acid's affinity for hard acid metals and Cu²⁺'s preference for square planar coordination was used as the basis of design. Although the sensor was designed to utilize the signal enhancement capabilities of FRET, quenching of both fluorophores occurred and proved to be the most sensitive means of quantifying Cu²⁺ binding. Nonetheless, the sensor provided a selective and sensitive response to Cu²⁺ at pH 7.0. Another FRET peptide metal ion sensor was designed with the help of a biological starting point, the mercury binding protein MerP. A sensitive FRET enhancement or "turn on" response was observed for Hg²⁺, as well as Zn²⁺, Cd²⁺ and Ag²⁺ in pH 7.0 solution. While a selective response for only Hg²⁺ was the ultimate goal of this study, this sensor is still an improvement over current systems which utilize a quenching mechanism for Hg²⁺ detection. While the previous studies investigated these sensors in aqueous solutions, the end goal was to devise a sensor based on an immobilized peptide chelator with FRET capabilities. To this end, immobilized, fluorophore labeled peptide studies were then conducted on Tentagel resin using a visible region FRET pair. A flow injection fluorescence analysis system using the immobilized fluorophore labeled peptide as the ion exchange material was also designed, allowing for the efficient analysis of fluorescence solutions. In addition to the work conducted with FRET sensors, studies were also conducted using magnetic [gamma]-Fe₂O₃ nanoparticles with PLCys immobilized onto the surface. The [gamma]-Fe₂O₃ nanoparticles are ideal supports since they can be magnetically collected and have a very large surface area to mass ratio. Finally, a method was developed to quantitatively screen metals bound to single Tentagel beads with immobilized peptides using ETV-ICP-MS. This method is an improvement over existing methods because it is nondestructive and simultaneously provides the absolute content of all metals bound.

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published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

No description available.

This dissertation describes the first high-precision observation of the infrared spectrum of the helium hydride molecular ion HeH⁺. The frequencies of five vibrational-rotational transitions in the range 1700-1900 cm⁻¹ in the X¹Σ⁺ ground electronic state of ⁴HeH⁺ have been measured to ±0.002 cm⁻¹ (±1 ppm). The Doppler tuned ion beam laser spectroscopic method was used in making the measurements: In a region of constant electrostatic potential, an HeH⁺ ion beam of several keV energy is intercepted at a small angle by a beam from a carbon monoxide infrared gas laser. The energy of the ion beam is adjusted to Doppler-shift an ion transition into resonance with a nearby laser line. On resonance the laser light stimulates transitions to take place. If the resonating states differ in population, the laser-induced transitions produce a net population transfer. The occurrence of population transfer is detected by monitoring the transmission of the ion beam through a gas target downstream from the laser beam interaction region. The transmission through the target is dependent upon the ion beam vibrational-state population distribution and therefore is sensitive to changes in the population distribution, because the cross-section for charge-exchange neutralization of an incident ion is dependent upon the vibrational state of the ion. The current interest in molecular ions in general, and in HeH⁺ in particular, is explained. The existing theory of the structure of HeH⁺ is summarized and a comprehensive listing of theoretical treatments of the structure of HeH⁺ is given. The meager previous experimental work on HeH⁺ is reviewed. The principles of the Doppler tuned ion beam laser resonance method are discussed and the experimental apparatus used is described in detail. The acquisition and analysis of the data is described and the results are compared with the best existing theoretical predictions of the transition frequencies. The present experimental values (given by D. E. Tolliver, G. A. Kyrala, and W. H. Wing, Phys. Rev. Lett. 43, 1719) for the measured transitions are (with the corresponding values calculated by D. L. Bishop and L. M. Cheung, J. Mol. Spectrosc. 75, 462, given in parentheses): (v,J)=(1,11)↔(0,12), 1855.905 cm⁻¹ (1856.152 cm⁻¹); (1,12)↔(0,13), 1751.971 cm⁻¹ (1752.198 cm⁻¹); (2,8)↔(1,9), 1896.992 cm⁻¹ (1897.139 cm⁻¹); (2,9)↔(1,10), 1802.349 cm⁻¹ (1802.492 cm⁻¹); and (2,10)↔(1,11), 1705.543 cm⁻¹ (1705.684 cm⁻¹). It is seen that the present experimental values deviate from the theory by typically 0.2 cm⁻¹, and are two orders of magnitude more precise than the theoretical values.

No description available.

The electronic structure and reaction dynamics of molecular and cluster anions in the gas phase has been investigated using negative ion velocity-map imaging photoelectron spectrometer. Photoelectron images provide important information about both energies and symmetries of the parent anion orbitals from which photoelectron originates. The symmetry and the ordering of several low-lying electronic states of neutral nitromethane (X¹A′, a³A″, b³A″, and A¹A″) are assigned based on a group theoretical analysis of the transitions angular distributions and the results of DFT calculations. The through-bond electronic coherence in meta- and para-dinitrobenzene anions is explored by recording a series of photoelectron images in 532-266 nm wavelength range. Photoelectron angular distributions for both isomers exhibit oscillatory behavior characteristic of the quantum interference effect, suggesting that dinitrobenzene anions retain their high symmetry electronic structures in the gas phase. Photoelectron imaging experiments on [O(N₂O)(n)]⁻, n =0–9 at 266 and 355 nm provide clear evidence of a switch from the cova)lent NNO₂⁻ cluster core to the atomic O⁻ core occurring between n = 3 and 4. The experimental results and theoretical modeling indicate that despite the greater stability of NNO₂⁻ relative to the O⁻ + N₂O⁻ dissociation limit, an O⁻ cluster core becomes energetically favored over NNO₂⁻ for n > 3, due to the more efficient solvation of the atomic anion. The photodissociation dynamics of I₂⁻ and IBr⁻ anions on the respective A' excited-state anion potentials is effectively unraveled in 780 nm pump - 390 nm probe time-resolve experiments. The time-dependent photoelectron spectra and classical trajectory calculations of the IBr⁻ dissociation provide the first rigorous dynamical test of the recently calculated A′ potential for this system. The photoelectron anisotropy cyclic variation observed in photodissociation of I₂⁻ is interpreted in the context of dual-center quantum interference model. The 390 nm pump – 390 nm probe experimental data reveal fast (≤100 fs) and delayed (~ 700 fs) appearance of the I⁻ channel in the photodissociation of I₂Cl⁻ and BrICl⁻ anions respectively. The difference in the reaction time-scales is attributed to the distinct dissociation pathways available for the anions to form I⁻ product.

It has been proposed to use heavy ion beams with energies around 10 MeV/amu, masses around 200, and average charges of 1+ as a driver for inertial fusion reactor. Current designs require the beams to travel through a region where the background gas pressure is several milli-torr. Thus, it is important to assess the rate at which the charge state of an incident beam evolves while passing through the background gas. The first objective of this project is to study the dependence of cross sections for multi-electron loss on target atomic number by using 6 MeV/amu Xe18+ ions and to compare the results with the n-body Classical Trajectory Monte Carlo calculations. A secondary objective of this project is to determine the extent to which the cross sections for molecular targets can be represented as sum of the cross sections for their atomic constituents. Cross sections for loss of one through eight electrons from 6 MeV/amu Xe18+ in single collisions have been measured with noble gas targets. The target Z-dependence of the total loss cross section was found to be well represented by two straight line segments. The cross section for He and Ne define one straight line segment and those for Ar, Kr and Xe define the other, where exhibits a smaller slope. The predictions of n-CTMC calculations are in good agreement with the measured total electron loss cross sections. A semiempirical fitting procedure based on the independent electron approximation provided a reasonably good representation of the individual cross sections for all of the noble gas targets. Additional measurements performed with a variety of molecular targets provided a rigorous test of cross section additivity and showed that the additivity rule works well for electron loss from heavy ions in the present energy and charge regime. A semiempirical calculation based the IEA shows that the average most probable impact parameter for electron loss is much smaller than the target molecular bond length. This result is believed to account for the finding of the insensitivity of the electron loss cross section to molecular structure.