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The rate and extent of intramolecular vibrational redistribution (IVR) following optical excitation in an isolated naphthalene molecule has been measured using the technique of supersonic free-jet spectroscopy. Naphthalene, exicted to its first (('1)B(,3u)) or second (('1)B(,2u)) excited singlet state is found to undergo a rapid vibrational redistribution which is quite global in nature. The rate of the IVR process is measured by observation of the fluorescence excitation linewidths as a function of vibrational energy (E(,v)). A smooth, monotonic increase in the vibronic linewidths as vibrational energy is increased is observed, corresponding to redistribution rates ranging from 9 x 10('10) sec('-1) at E(,v) = 3068 cm('-1) to 7 x 10('11) sec('-1) at E(,v) = 5200 cm('-1). The extent of the redistribution is monitored via single vibronic level fluorescence spectra of naphthalene taken in a free-jet. At low vibrational excitation the fluorescence spectra display sharp, well resolved features, indicating that little redistribution has occurred on the time-scale of the fluorescence (nsec). However, at energies above E(,v) = 2122 cm('-1) the spectra become diffuse. Computor modeling of these spectra shows that many zero-order levels must be involved in the redistribution process, at least all of the quasi-resonant levels of the same symmetry as the originally pumped level. Therefore, even at moderate vibrational energies, an isolated molecule the size of naphthalene undergoes a rapid flow of vibrational energy among much of the energetically available vibrational phase space, following optical excitation.

The uses of resonance enhanced two-photon ionization (R2PI) for studying unimolecular energy redistribution of molecules in a supersonic molecular beam is explored. The R2PI process relies on initially exciting a molecule to a state that is stable with respect to the up-pumping rate of an ionizing laser field. For such situations, the ion signal produced is proportional to the population of the intermediate state. It can therefore be used in place of the observation of emitted light for measuring the population of an excited state. This is particularly useful for states that do not radiate. The pulsed valve used to create the molecular beam is described in detail. Several experiments, undertaken to characterize the types of information that might be obtained, are described. From these it was determined that the R2PI technique has a detection efficiency of almost 100%. In addition, at laser fluences less than those required to saturate the first, resonant step, only the parent ion is observed. The technique has been shown to be useful for recording electronic absorption spectra with 1 cm('-1) precision, both for molecules with long singlet lifetimes (longer than the 4 nsec laser pulse width) and for molecules with very short singlet lifetimes (up to three orders of magnitude shorter than the laser pulse width). The ionization threshold for a large polyatomic molecule, naphthalene, has been determined to a precision greater than previously reported. A two-laser experiment is also described in which the decay of unperturbed singlet and unrelaxed triplet states are observed. This experiment can easily be extended to provide sufficient information, with the addition of a single independently determined quantity, to completely characterize the intramolecular energy redistribution in molecules.

Time-of-flight detected resonant two photon ionization (R2PI) in supersonic beams is investigated. The advantages of the method are the high sensitivity, spectral selectivity and the lack of extensive fragmentation in the mass spectra. To obtain these properties the molecular system must meet several restrictions. Stable intermediate electronic states, which are greater than half of the adiabatic ionization energy generally are detected with these advantages, with a single photon field supplying the energy to populate the intermediate state and to form the photoions. Modulation of the ionization efficiency is observed when a rapid decay channel is available to the intermediate state, which is no longer coupled to the photon field. These properties are illustrated by the behavior of aniline, bromobenzene, and metal carbonyl systems. Two-color ionization removes many of the restrictions inherent to one-color R2PI. High efficiency is maintained for a broader class of molecules by allowing the ionization photon to provide the energy spanned by the intermediate state and the ionization continuum levels. Experiments which scan the ionization laser energy, provide information regarding the nature of the ionization step in benzene and napthalene. The predominantly step-like direct ionization structure observed, indicates that this is the dominant ionization process. Thus the relevant selection rules governing the propensity of an intermediate state to ion transitions are largely of a vibrational nature. The two-color ionization method has been specifically applied to studies of collision-free vibrationally excited triplet state levels formed in the molecular beam. By varying the time delay between the pump and ionization lasers, the decay of excited state populations can be monitored. This time evolution data has been unavailable through conventional methods due to the experimental difficulties imposed by the long-lived, non-fluorescent nature of these states. As the decay rate of these states are highly sensitive to excess vibrational energy, the presence of collisional perturbation tends to distort the true non-radiative decay rates. In the molecular beam environment, the decay of triplet levels, isoenergetic with initially pumped S(,1) vibronic states, have been monitored as a function of the excess vibrational energy in several aromatic systems. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

This dissertation presents the results of chemical research efforts directed in three areas: (1) the final design of an ultraviolet-visible absorption and emission matrix isolation apparatus is described, (2) by employing this apparatus, molecular scale interactions of the 1:1 metal-water adduct are investigated utilizing electronic absorption spectroscopy, and (3) molecular orbital and electronic state-to-state correlations are invoked to interpret the chemical reaction dynamics of the adducts along ground and excited potential energy surfaces. The final design of this matrix isolation apparatus incorporated unique features that abbreviated data acquisition time and obviated several experimental problems that have plagued previous matrix isolation studies. The investigations of the molecular interactions and reactions of the Group IIA metal atoms (Mg, Ca, Sr, Ba), the Group IIIA metal atoms (Al, Ga, In), and the Group IVA metal atoms (Si, Ge, Sn, Pb) with water molecules isolated in rare gas matrices at 15 K are reported. In most instances, the strength of the metal-water interaction is sufficiently strong to perturb significantly the electronic structure of the metal atom which results in a unique band structure for the adduct that is red-shifted from the metal atomic resonance transition. Selective photolysis studies contributed to a better understanding of the electronic structure of the adduct. Molecular orbital theory is invoked to interpret the nature of the ground and excited states of the metal-water adduct. By resorting to molecular orbital and electronic state correlation methods, the qualitative features of the metal-water interaction potential energy surfaces are derived which predicate the chemical reaction dynamics that, in turn, result in a fundamental understanding of relative reactivities, photochemical pathways, and chemiluminescent processes. In addition, this dissertation reports studies of the electronic structures of the Group IIIA metal suboxides (Al(,2)O, Ga(,2)O, In(,2)O) in absorption and emission. Progressions in the symmetric stretching and bending modes for the ground and excited states are observed. Finally, previously undocumented electronic structures of several metal dimers (Al(,2), Ba(,2), Ge(,2)) are reported and discussed.

Resonance enhanced two-photon ionization (R2PI) has been developed as an analytical detection in supersonic molecular beams and subsequently applied to current problems in molecular spectroscopy and excited state dynamics. The method consists of tunable dye laser ionization followed by time-of-flight mass spectroscopy detection of ions. Ionization requires resonant absorption of two photons and so the method is selective for molecular resonances. Parent ions only are formed which makes detection and identification straightforward. Such resonant ionization with commonly available laser powers can approach unit detection efficiency, which makes the technique suitable for environments with low sample densities. It is especially useful for systems which for various reasons cannot be studied by fluorescence. This technique has been applied to the S(,1) spectroscopy of bromobenzene and naphthalene and to the spectroscopy of naphthalene and benzene near the first ionization potential. It has also been used to measure excited state lifetimes for the statistical limit molecules benzene and toluene and for the intermediate case molecules biacetyl and benzoquinone. The triplet lifetimes of toluene and benzene are much shorter in the collision-free environment than previously estimated, due to intersystem crossing to the ground state which is promoted by vibrational energy in the triplet manifold. The dependence of the rate of intersystem crossing for toluene on triplet vibrational energy is not as steep as expected from current theories, due to intramolecular vibrational relaxation in the triplet manifold. Biacetyl and benzoquinone decays can both be described in the intermediate strong coupling case, although weakly coupled triplet states are also necessary in the decay scheme. The non-radiative decay rate of benzoquinone, unlike that of toluene, increases exponentially with vibrational energy in the triplet manifold. The successful application of the R2PI technique in these experiments, as well as others which have been attempted, demonstrate that this is a versatile method which will continue to be important in basic research and in practical analytical chemistry.

An experimental investigation was performed to determine the drift velocities of oil slicks and the pile up of oil layers against barriers in the presence of water waves. Other investigations of the drift response were made by substituting thin plastic sheets in place of the oil slicks. Parameters were developed which govern these movements. Discrepancies in the literature between drift of oil lenses and the "Stokes' drift" were solved. It was discovered that the boundary layer between the drifting oil slick and wave motion has turbulent character and is not laminar as was derived from theory and assumed to be the case.