Anodic sulfide films on antimony metal have been studied in relation to their electrochemical and photoelectrochemical properties. The formation of the anodic films in aqueous hydrosulfide solutions has been investigated using potentiodynamic, galvanostatic and potentiostatic techniques. The sulfidation mechanism and the efficiency of charge storage in the surface phase was found to be strongly dependent on the electrode potential and current density. The initial stages of formation followed a high field growth process involving ionic migration through the film. For thicker films, the growth rate was controlled by a chemical step involving mass transport and nucleation processes. Metal dissolution accompanied film formation under most growing conditions. The electronic and potential distribution at the sulfide/solution interface have been examined using a. c. impedance measurements. The charge distribution across the film exhibited a strong influence on the electrochemical behavior of the system. A band model has been used to describe the potential arrangement in the space-charge region near the surface. The sulfides possessed n-type semiconductor properties and this conductivity has been correlated to their non-stoichiometric nature. The donor density has been estimated from Mott-Schottky plots to be approximately 2 x 10('20) cm('-3). The solid-state characteristics of the films were investigated using photocurrent and photopotential methods. The development of photosensitivity has been discussed in relation to the growth behavior. The optical properties that give rise to the photoactivity has been determined from the spectral response of the photoeffects. The light absorption process has been found to involve phonon assisted excitations. The fundamental band edge for the indirect transitions was calculated to be near 1.77 eV.

A computer controlled infrared color center laser has been developed primarily for the purpose of studying free radicals in the gas phase and has been applied to the study of the C(,2)H radical. The laser spectrometer, based on a commercial Burleigh FCL-20 color center laser, has been shown to be a stable, single frequency, tunable, c.w. infrared source capable of continuous scans of 10 cm('-1) or more with resolution of 10 MHz or better. A number of tests were performed to determine the sensitivity of the spectrometer. Noise limitations inherent to color center lasers have been overcome by combining the color center laser spectrometer with sensitivity enhancement techniques. These techniques include multi-pass absorption, Stark modulation, magnetic rotation, and frequency modulation. Experiments were conducted to test the combination of these techniques with the spectrometer. It has been found that magnetic rotation spectroscopy combined with multi-pass methods offer greatly increased sensitivity along with the advantage of being selective to only paramagnetic species, such as free radicals. Using this computer controlled color center laser spectrometer, the free radical C(,2)H has been detected in a discharge of argon over polyacetylene. This is the first reported gas phase absorption spectra of the vibrational and electronic transitions of C(,2)H. The C(,2)H radical was extensively studied in the 4200-3580 cm('-1) region. A rich spectrum has been observed, with typical line density of 1 or 2 lines per cm('-1), most of which have been assigned to argon transitions. A number of regular bands have been detected in this region, of which five have been firmly assigned to C(,2)H. These bands are centered at 3693, 3772, 3786, 4012, and 4108 cm('-1). The 3772 cm('-1) band has been assigned to the transition from the first excited bending mode of the ground state to the first excited bending mode of the A('2)(PI) electronic excited state. The 3786 cm('-1) band has been tentatively assigned to the origin band of this electronic transition while the remaining bands have been assigned to ground state vibrational transitions. The rotational and vibrational nature of these bands has been determined. Estimates of all three vibrational frequencies have been made, with (nu)(,1) = 3625 cm('-1), (nu)(,2) = 375 cm('-1), and (nu)(,3) = 1860 cm('-1). This is the first reported estimate of the bending frequency, (nu)(,2).

The OH stretching fundamental ((nu)(,1)) of hydroxylamine has been studied using a computer controlled color center laser spectrometer. Absorption and Stark modulated spectra were obtained in the spectral region 3620 to 3710 cm('-1). The spectra is dominated by many strong perpendicular type Q branches and exhibits both parallel and perpendicular type lines. A large number of lines have been assigned and a nonlinear least squares fit results in ground and excited state constants. The spectrum of hydroxylamine exhibits many small perturbations, presumably caused by interaction of the (nu)(,1) level with combinations of lower energy vibrational modes. A hot band, wherein the (nu)(,9) torsional motion is excited in both the ground and excited state has been identified and assigned. All lines are believed to originate from the trans form of hydroxylamine and no lines confirming the existence of the cis isomer were observed. A commercially available single mode ring dye laser has been computerized and used in the investigation of the effects of applied electric and magnetic fields on the polarization of laser light propagating through a low pressure sample of NO(,2). Stark polarization spectroscopy has been shown to provide a great simplification of the complex visible absorption spectrum and arises largely due to the combination of Stark mixing and Zeeman nonlinear level crossing phenomena.

Rotational or rovibrational spectra of the free radicals NH(,2), BO(,2) and NO(,2) have been taken using various high resolution laser techniques. The hyperfine structure of the u state of NH(,2), tentatively assigned as 2(,20), J = 3/2, (')X('2)B(,1) (0,13,0), has been obtained from an analysis of the microwave optical double resonance signals which occur between the u state and the J = 1/2 spin component of 1(,10) in (')A('2)A(,1) (PI)(0,10,0). The similarity of the ('1)H hyperfine splittings in u with those of the 2(,20), J=3/2 rotational level of the (')X('2)B(,1) (0,0,0) state supports the assignment of u to a highly excited vibrational state of (')X('2)B(,1). The ('14)N hyperfine splittings were found to be about 1 MHz. These splittings are considerably smaller than those of 2(,20) (')X('2)B(,1) (0,0,0). This difference has been attributed to the fact that the hyperfine coupling constants of (0,13,0) must be averaged over a large amplitude bending vibration and to the presence of borrowed (')A('2)A(,1) character in the u state. The hyperfine structure of 37 R-branch transitions involving several vibronic bands in the ground and excited electronic states of ('11)BO(,2) has been observed with intermodulated fluorescence detection saturation spectroscopy. Stabilization of the dye laser and the elimination of spectral power broadening has permitted the achievement of linewidths of better than 10 MHz. A set of hyperfine constants for both electronic states has been determined from the observed splittings. The (nu)(,1) + (nu)(,2) + (nu)(,3) combination band of NO(,2) has been investigated using a color center laser spectrometer with magnetic rotation sensitivity enhancement. The electron spin fine structure of this band has been resolved for the first time. The fine structure constants obtained for (1,1,1) expressed as differences from the corresponding ground state values are (DELTA)(epsilon)(,aa)=0.0115(5), (DELTA)((epsilon)(,bb) + (epsilon)(,cc))/2= -3.6(11) x 10('-5), and (DELTA)(DELTA)(,K)('s)= -4.0(6) x 10('-5) in cm('-1). Analysis of the magnetic rotation spectrum in combination with the previous high resolution data provides improved K dependent rotational (A) and centrifugal distortion constants ((DELTA)(,K), H(,K), (DELTA)(,NK), and H(,KN)). The lineshapes in magnetic rotation were observed to depend significantly upon the experimental conditions. These lineshape effects limited the accuracy of the magnetic rotation data and suggest a need for precise control of operating conditions.

Techniques are described for studying reactive species, in particular radicals and metal clusters but generalizable to most molecules which can be made by photolytical processes from stable precursors. Methods for radical formation in a supersonic molecular beam by laser photolysis are described. The B(<---)X transition in methoxy radical has been vibrationally and rotationally resolved and is discussed. Electronic, vibrational and rotational cooling of the radical is shown to be substantial with this technique. Laser vaporization combined with molecular beam techniques are described as they can be applied to metal cluster studies. Ionization potentials have been bracketed for clusters of copper up to 28 atoms. The potentials approach that of the bulk metal as the cluster size increases but for Cu(,28), there still remains a significant difference from the work function of the bulk metal. Copper dimer electronic spectra in the visible and ultraviolet regions have been studied and several new band systems have been seen. An observed long ground state progression is believed to be due to a very tightly bound excited state of the dimer. Two interacting states are observed and the resulting perturbed levels are modeled with a simple pair wise interation. Other fragmentary systems and previously seen visible systems are also discussed.

We developed an ultrasensitive, computer-controlled, visible/near-IR, cw laser photoacoustic spectrometer capable of detecting forbidden transitions in order to understand the nature and states of highly vibrationally excited molecules. We have obtained nearly Doppler-limited survey spectra of highly vibrationally excited alkynes over a considerable energy range. Acetylene and substituted acetylenes (HCCR) comprise a novel group of molecules because the highly localized CH chromophore (CH oscillator) is linearly coupled via a strong CC triple bond to the rest of the molecule. Thus, these HCCR alkynes are essentially one dimensional molecules particularily amenable to studies involving intramolecular energy redistribution. We first studied acetylene (H('12)C('12)Ch) and four isotopic modifications (H('12)C('13)CH, H('13)C('13)CH, H('12)C('12)CD, D('12)C('12)CD) to understand the global pattern (spectral positions, assignments, intensities, and perturbations) of vibrational transitions in simple, model polyatomic molecules at high levels of vibrational excitation and to develop comparison data for spectral analyses of substituted acetylenes which exhibit intramolecular vibrational mixing and energy redistribution. The second phase of our studies was to obtain detailed spectroscopic information on the overtones of the following substituted acetylenes (HCCR): cyanoacetylene (HCCCN), methylacetylene (HCCCH(,3)), 3,3,3-trideuteromethylacetylene (HCCCD(,3)), 3,3,3-trifluoromethylacetylene (HCCCF(,3)), and tertiary butyl acetylene (HCCC(CH(,3))(,3)). The substituent group "R" was varied from a simple H atom to a tertiary butyl group to study not only the effect of increasing density of states but to understand and distinguish the necessary and sufficient causes of irreversible intramolecular energy redistribution in highly vibrationally excited states of isolated polyatomic molecules as a function of increasing molecular complexity.

The cooling capabilities of supersonic expansions provide a powerful tool for investigating polyatomic molecules. Complex, optical spectra of room temperature molecules can be enormously simplified by the supersonic jet method. In recent years, this technique has provided a wealth of new information concerning the structure and dynamics of a wide class of molecules. A new technique has been developed to produce interesting species which do not readily exist under normal laboratory conditions. In particular, a pulsed laser is used to vaporize bulk metal material in conjunction with a supersonic expansion. The latter cools the hot metal vapor where clustering of metal atoms occur. In this fashion, clusters of refractory metals such as Ni(,x), Fe(,x), Mo(,x) and W(,x) have been readily produced. Spectral investigations using mass selective photoionization of Cu(,2), Ag(,2), Mo(,2) and Cu(,3) have been performed. The resulting spectra have been used to characterize the internal energy of jet-produced metal clusters. In addition, the spectra have been examined for new information regarding the electronic structure of these molecules.

Emission at the Na D lines has been observed from the intersection of crossed molecular beams of K and NaCl irradiated by a CW dye laser at wavelengths from 590 nm to 735 nm. The three-beam signal exhibits a threshold near 735 nm and is linearly dependent on the laser and molecular beam intensities. This three-beam signal has been observed under experimental conditions in which all two beam signals are accounted for, and is attributed to the formation of Na* by photoexcitation of the KNaCl reaction complex. The effective two-body cross section for the process is approximately 10('-21) cm('2) in a laser field of 1.5 kW/cm('2).

Relaxation processes in pyridine and pyridazine have been investigated using time resolved spectroscopic methods. In order to investigate the photophysics and dynamics of molecular excited states a versatile transient absorption spectrophotometer has been designed and constructed to study low pressure gas phase samples on the nanosecond time scale. The sensitivity of this apparatus is high enough to allow investigation of samples with a (DELTA)(epsilon)p > 0.05 M('-1)cm('-1)Torr('-1), and has an rms noise level of (TURN)0.0002 absolute absorbance units. With this spectrophotometer a T(,n)()T(,1) intersystem crossing, and has an estimated oscillator strength of (TURN)0.02. An internal calibration method has enabled reliable excited state extinction coefficients to be evaluated. The intersystem crossing process in pyridine has been shown to be in or very near the statistical limit. Pressure-dependent and nonexponential nonradiative decay is exhibited by triplet pyridine. These two forms have intrinsic lifetimes of > 10 (mu)s and 200 ns. A weak complex is found to be formed between triplet pyridine and oxygen in the quenching process. Gas phase ground state repopulation experiments show that S(,o) pyridine is the resulting state of this quenching process. Total repopulation of vapor phase pyridine has also been observed in the presence of 10 Torr cyclohexane and 100 Torr O(,2) on the (mu)s time scale. A 4% (+OR-)2% photochemical yield has been calculated for pyridazine following excitation to the S(,1) state. A dual component transient of pyridazine is found to absorb in the region of 26,640 cm('-1) to 27,200 cm('-1). This is either vibrationally excited ground elctronic state molecules formed from two channels one of which is S(,1), the other of which has a lifetime of 280 ns, or it is vibrationally excited ground electronic state pyridazine and an intermediate in the photochemical process. Ground state repopulation experiments indicate the formation of a transient having (epsilon) > 590 M('-1)cm('-1). This transient is present even in the presence of 400 Torr of added SF(,6).

The passivity of iron in borate buffer solutions and its breakdown in presence of sulfide ions was studied using standard electrochemical techniques (e.g., galvanostatic, potentiodynamic, potentiostatic) and complemented with microscopic examination and electron microprobe analysis of the surface. Mass transport effects and the nature of dissolved species were investigated using rotating disc and ring-disc electrodes. The electronic properties of the oxide film, and their relationship with the breakdown of passivity, were studied using photoelectrochemical techniques. Initial passivation of iron in sulfide-containing solutions is due to coverage of the surface by an iron(II) oxide phase, which competes with the formation of a non-protective iron sulfide (mackinawite) film. The passive layer is gradually converted into non-stoichiometric (gamma)-Fe(,2)O(,3). This oxide is an n-type semiconductor. At higher positive potentials, mackinawite is oxidized to Fe(,2)O(,3) and S. Sulfur can also be produced by direct oxidation of HS('-), and FeS(,2) (pyrite) can precipitate from the solution. The resistance of the passive film to breakdown is affected not only by its thickness, but also by its composition (expressed as deviation from stoichiometry). Both are controlled by the potential at which the electrode is passivated and the time of passivation prior to sulfide injection. The mechanism of localized corrosion on passive iron is associated to the formation of mackinawite patches on the surface. The extent of corrosion is determined by the kinetics of nucleation and growth of mackinawite. The nucleation of mackinawite patches, is a fast process related to the adsorption of HS('-) on weak spots of the passive film. The growth of the nuclei occurs by dissolution of the adjacent oxide, and its rate is controlled by the diffusion of Fe(II) species away from the surface. Pitting corrosion occurs underneath the mackinawite deposits by a mechanism similar to that of crevice corrosion.