The first investigation of the adsorption of water on diamond (100) by infrared multiple-internal-reflection spectroscopy using a natural type IIa diamond internal reflection element is reported. Following exposure to water at elevated temperatures, infrared absorption features are observed at 1250 and 1200 cm$\sp{-1}$; 1125 and 1080 cm$\sp{-1}$; and 720 cm$\sp{-1}$, and assigned to ether (C-O-C), hydroxyl (C-OH), and carbonyl ($>$C=O) modes, respectively. It is thought that water adsorbs dissociatively and at higher temperatures the adsorbed hydroxyl species further decompose to ether, carbonyl, and hydride surface species. The substantial observed reactivity of diamond with modest exposures to water indicates a potentially important role for surface hydroxyl and oxide species in the surface chemistry of diamond films grown by chemical vapor deposition. Direct evidence for the diamond surface hydride structures, obtained by deuterium substitution, is also presented. Infrared evidence is seen for both monodeuteride and dideuteride surface structures, with one or two deuterium atoms per surface carbon atom ($\delta\sb{\rm CD}$ mode at 901 cm$\sp{-1}$ and $\delta\sb{\rm CD\sb2}$ mode at 1125 cm$\sp{-1}$, respectively). The thermal stability of oxides on diamond (100) was investigated by annealing experiments. Infrared modes assigned to hydroxyl and carbonyl species disappear, presumably via desorption, upon heating the oxidized diamond surface above 1000$\sp\circ$C. Finally, surface reactions induced by exposure to a hot acid solution used to etch graphite from diamond were also investigated by infrared spectroscopy. The primary absorption band at 1020-1120 cm$\sp{-1}$ is assigned to hydroxyl groups and infrared absorptions near 1250 cm$\sp{-1}$ are assigned to ether groups. We conclude that the acid solution oxidizes the diamond surface.

Dissociative Resonance Raman Spectroscopy has been used to probe the dissociation dynamics of two different molecules, dimethyl zinc and methyl mercaptan. A method for analytically describing potential energy surfaces by the use of rational approximants is described. A rigorous, systematic algorithm to remove spurious singularites from such approximants is presented. A tunable, narrow band UV laser system has been developed capable of generating 10 nsec pulses of 10 mJ energy, with a bandwidth of less than 1 $\rm cm\sp{-1}.$ The tuning range of the ArF final amplifier is 192 to 194 nm, and use of a stimulated Raman scattering cell allows for tuning up to 205 nm at 0.5 mJ energy per pulse. The Raman spectrum of DMZ is complicated by the appearance of Zn atom and ion lines. The fundamental and 1st overtone of a methyl umbrella mode are the only Raman features seen. The Raman spectrum of methyl mercaptan shows a progression which we assign to the C-S stretching mode. A strong feature we assign to the S-H stretching fundamental exhibited no overtones. Our results show that a previous assignment from a low resolution spectrum taken in another laboratory is erroneous. Methyl mercaptan's Raman spectrum is complicated by the appearance of CS fluorescence and atomic carbon fluorescence. A pathway is proposed for the multi-photon formation of these emitting species at 193 nm.

Theoretical calculations for the ground states of arsine (AsH$\sb3$), trimethylgallium (TMG) (Ga(CH$\sb3$)$\sb3$), the arsine$\cdot$TMG adduct, gallane (GaH$\sb3$), the gallane$\cdot$arsine adduct, small Ga$\sb{x}$As$\sb{y}$ clusters (x = y; x = 2-4), and small gallium hydrides are carried out at the self consistent field (SCF) Hartree-Fock level of theory, using analytic energy gradients for rapid geometry optimization. In addition, the SCF results are compared with theoretical predictions obtained at the coupled cluster level of theory including all single and double excitations, (CCSD). The precursors to the formation of GaAs, arsine and TMG, were determined to be of C$\sb{3v}$ and C$\sb3$ symmetries, respectively, while gallane was found to be D$\sb{3h}$ The equilibrium structures for Ga$\sb2$As$\sb2$, Ga$\sb3$As$\sb3$, and Ga$\sb4$As$\sb4$ are found to be of D$\sb{2h}$, C$\sb1$, and C$\sb{i}$ symmetry, respectively. The adduct binding energies and vibrational frequencies (SCF) are also obtained resulting in two stable bonded adduct species, arsine$\cdot$TMG of symmetry point group C$\sb3$ and arsine$\cdot$gallane of C$\sb{3v}$ symmetry. Finally, our theoretical predictions support a slightly exothermic gas-phase reaction yielding GaAs through a TMG$\cdot$AsH$\sb3$ adduct which is formed without an activation barrier.

While the dynamics of model systems has been widely studied, the sizes of the systems has been limited. We present the dynamics for two large systems: a 9 degrees of freedom molecule and a 10000 state tier model. Classical non-linear resonance analysis and its quantum analog have been instrumental in providing insight into the pathways and rates of IVR processes in the overtone excitation of small molecules such as benzene and cyanoacetylene. It has been observed that the fourth overtone OH excitation of propargyl alcohol (PPA) is anomalously broad in comparison to the corresponding band of other small alcohols, possibly the result of rapid IVR out of the excited mode. An accurate model displayed no classical relaxation, but the quantum dynamics indicated an approximate degeneracy between the excited OH stretch and a combination band that can explain the observed broadening. To better understand the tier-to-tier relaxation process, an abstract model consisting of ten tiers of states was developed with the final tier representing the vibrational bath-states via a 50 state/cm$\sp{-1}$ state density. The survival dynamics showed irreversible relaxation out of the initial tier without the usual Poincare recursions. Interestingly, a calculation of the time-dependent spectrum showed the presence of only a few large features up to 720 fs which could not be attributed in a simple fashion to the dynamics of sub-models consisting the first n tiers. The early appearance and long persistence of a few broad bands implied the presence of "IVR resonances". In an attempt to elucidate these resonances, a imaginary damping function or optical potential was added to the model. An eigenvalue calculation on the resulting Hamiltonian did yield several long-lived resonances, and in fact, a spectrum calculated using only the first five resonances qualitatively reproduced the short pulse-length spectrum calculated from the original model. The "discovery" of these resonances is a step towards understanding and interpreting future pulselength dependent spectra in terms of the underlying tier structure of the systems studied.

FT-ICR studies of high mass $\rm (C\sb{>150})$ carbon clusters have brought insight to the controversial structures of carbon fullerenes. Laser vaporization followed by supersonic beam technique produced carbon clusters that directly injected into the bore tube of a 6 Tesla magnet. Mass spectra of the trapped cluster ions reveal the presence of only even-numbered clusters in the low mass regions, thus verifying the predominance of graphite closed shells. It is believed that the larger clusters also exist as aggregates loosely bound to each other on their surfaces and will readily disaggregate upon evaporation. When clusters of size C$\sb{300}$ or larger are fragmented by excimer laser, the products are mostly even-numbered ions resulting from C$\sb2$ loss which satisfy the retention of a fullerenes structure. In addition, there are distributions of multiply-charged high mass positive clusters detected as the photofragments undergo thermionic emission. This fragmentation experiment is currently used to compare the hypotheses of (1) giant fullerenes model where carbon condenses to form empty hollow cages of large radii, (2) aggregation of small clusters by van der Waals forces to form high mass clusters, and (3) "Russian-egg" model where high mass clusters exist as concentric closed shells.

A fundamental and long-standing question surrounds the mechanism of primary bond cleavage in azoalkanes: do the two C-N bonds break in a synchronous or a stepwise manner? When a vapor phase azoalkane absorbs near ultraviolet light, it dissociates into two alkyl radicals and nitrogen. Transient CARS spectroscopy was used here as a time-resolved probe of the photoproducts formed from azoalkanes excited at 355 nm. In a detailed reinvestigation, azomethane was found to dissociate in a stepwise process involving a methyldiazenyl radical intermediate. The diazenyl intermediate was formed in less than 1 ns and lived for 5.3 $\pm$ 1 ns before fragmenting into a methyl radical and nitrogen. Kinetic studies on azoisopropane (AIP) also gave evidence for stepwise photodissociation with a similar diazenyl lifetime. The first methyl radical formed in azomethane photodissociation was found to have 0 to 4 quanta of $\nu\sb2$ excitation, whereas the second methyl radical was predominantly vibrationally unexcited. The nascent rotational temperature of N$\sb2$ from azomethane was found to be 2500 K, and its vibrational distribution was confirmed to be 84% in v = 0 and 16% in v = 1. These results seem consistent with predictions based on the transition state structure computed for methyldiazenyl dissociation. Internal energy distributions were also measured for the nitrogen formed from 3-(methylazo)-3-methyl-butene (MAMB), which was previously shown to undergo stepwise dissociation through a methyldiazenyl intermediate. The rotational and vibrational energy distribution from MAMB were almost identical to those from azomethane, consistent with a common dissociation mechanism. AIP also gave similar nitrogen rotational and vibrational distributions, suggesting that the dissociative transition state of isopropyldiazenyl is similar to that of methyldiazenyl. In summary, direct kinetic measurements have demonstrated stepwise gas phase photodissociation in acyclic azoalkanes. Related measurements of product internal energy distributions should form the basis for a detailed dynamical understanding.

Molecular beam chemiluminescence from Na$\sb2$ + F $\to$ NaF + Na$\sp\*$ was dispersed and measured with a fast spectrograph. Attention was given to emission wavelengths at and around 388.5 and 342.8 nm, which correspond to the electric dipole forbidden atomic transitions Na 4s $\to$ 3s and 3d $\to$ 3s, respectively. It was hoped that the nascent products NaF and Na$\sp\*$ would interact such that these normally dis-allowed transitions could be observed, thereby constituting a direct glimpse of the three atom system late in the reaction event. A small emission peak was observed at the 3d $\to$ 3s transition wavelength, but its weak intensity could be explained by electric quadrupole radiation of the free atom rather than a reaction-induced breaking of dipole selection rules. No structured emission was observed at the 4s $\to$ 3s wavelength, although interference from Na$\sb2\sp\*$ may be obscuring an otherwise observable peak. In a second experiment, two lines of an argon ion laser are crossed with a single Na/NaCl beam in an effort to observe resolved laser-induced fluorescence of the stable molecule Na$\sb2$Cl. The copious emission from Na$\sb2\sp\*$ precluded any definitive identification of fluorescence from the target molecule. Finally, a detailed description is given of the f/2 spectrograph that was developed in this laboratory. The instrument observes a 100 nm wavelength region simultaneously, images atomic lines to a full-width-half-maximum (fwhm) of 2 nm, has a photocathode quantum efficiency of 3.1% at 800 nm, and exhibits only 36 counts per second dark current.

Photoelectron spectra of negatively charged iron, cobalt and nickel clusters in the size range of 5 to 20 (4 to 26) and 5 to 20 atoms respectively have been obtained. The electron affinity (E.A.) values along with the reported ionization potential (I.P.) have been used as a probe of the valence electronic structure of these clusters. This information is further used to understand the reactivity of the neutrally charged counterpart clusters of iron, cobalt and nickel with dihydrogen. An excellent anticorrelation between an empirically determined quantity called Ep, defined as IP $-$ EA $-$ e$\sp2$/r, and the reactivity of these clusters is observed. Ep is a direct measure of the polarizability of the clusters; The excellent anticorrelation is consistent with the Pauli Repulsion mechanism and is found to be a significant factor in controlling the reactivity of these clusters.

High resolution infrared diode laser kinetic spectroscopy has been used to investigate the properties of C$\sb2$H reaction kinetics. The ethynyl radical (C$\sb2$H) was produced in a flowing system by excimer laser photolysis (ArF, 193 nm) of either CF$\sb3$CCH or C$\sb2$H$\sb2$ and the transient infrared absorptions of C$\sb2$H or possible reaction products were followed with the diode laser probe. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. Only two reaction products were observed, CO and CO$\sb2$, with the amount of CO produced being about five times larger than the amount of CO$\sb2$ produced. Both products are produced in vibrationally excited states. CO$\sb2$ was produced long after C$\sb2$H reacted and thus is not a product of the direct reaction. Two processes leading to CO formation have been observed: a fast, direct process for which the rate of CO appearance approximately matches the rate of C$\sb2$H decay and a much slower indirect process. The fast process produces vibrationally excited CO (v = 5 $\gets$ 4 and higher). The indirect process is observed to be dominant for the lower vibrational transitions and its rate exhibits saturation with increasing O$\sb2$ pressure. In order to approximate these kinetics, it appears that at least two intermediates between C$\sb2$H and CO must be involved for the indirect process. In other kinetic studies, the rate constants of C$\sb2$H reactions were measured to see if other C$\sb2$H reactions might exhibit addition channels. The time decay of a C$\sb2$H infrared absorption line originating from the ground vibronic state was monitored as a function of reactant pressure to determine a second order rate constant. When possible the dependence of the reaction rate on helium pressure was investigated over the range of 8-70 Torr. Second order rate constants of 3.0(2) $\times$ 10$\sp{-12}$, 1.3(3) $\times$ 10$\sp{-10}$, 3.6(2) $\times$ 10$\sp{-11}$, 4.4(4) $\times$ 10$\sp{-13}$, 2.3(3) $\times$ 10$\sp{-13}$ cm$\sp3$ molecule$\sp{-1}$ s$\sp{-1}$ were obtained for the reactions of C$\sb2$H with CH$\sb4$, C$\sb2$H$\sb4$, C$\sb2$H$\sb6$, H$\sb2$ and D$\sb2$ respectively. A third order rate constant of 2.1(3) $\times$ 10$\sp{-30}$ cm$\sp6$ molecule$\sp{-2}$ s$\sp{-1}$ was obtained for the reaction of C$\sb2$H with CO.

Symmetric-top molecules (CF$\sb3$Br, CF$\sb3$Cl, CF$\sb3$H and CH$\sb3$Br) in a seeded supersonic nozzle beam are orientation selected by a hexapole electric field, and collide at a right angle with fast (3-40 eV) potassium atoms. The ionization reactions at two different molecular orientations are studied: $$\eqalign{&\rm K + CX\sb3 - Y \to K\sp+ + CX\sb3 + Y\sp-\qquad (Tails\ Orientation)\cr &\rm K + Y - CX\sb3 \to K\sp+ + CX\sb3 + Y\sp-\qquad (Heads\ Orientation)\cr}$$ We observed that collision ionization reactions are influenced greatly by molecular orientations. For CF$\sb3$Br, CH$\sb3$Br and CF$\sb3$Cl, the reactivities are greater with the heads orientation than that with the tails orientation, but for CF$\sb3$H, the H end is unreactive. The steric effects are more pronounced at the low energy end near the thresholds, and almost disappear at energies above 20 eV. Most importantly, we also found that the energy thresholds of these reactions are different for heads and tails orientations, indicating that the electron affinity of a molecule should be considered as an anisotropic parameter. Some features of the experimental results are explained by the Harpoon Electron Transfer model. Further theoretical and experimental studies are required for the fully understanding of the reaction dynamics.