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Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical technique with widespread applications. In this work, SERS applications in the realms of art conservation and biosensing are reviewed. First, the theory of this unambiguous and ultrasensitive technique is explained. Next, a review of the pedagogical journey in art conservation research through the lenses of undergraduates is offered in Chapter 2, a chapter recently submitted to the American Chemical Society. Finally, an investigation in biosensing SERS is explored with developing a SERS pH sensitive probe while offering new insight into SERS capabilities and the relationship between analyte and nanoparticle.

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Part I. The Eley-Rideal reaction of H atoms with Cl adsorbed on Au(111) surface is examined. Electronic structure calculations based on density functional theory are used to construct a model potential energy surface. Both a flat and corrugated surface are considered. Single adsorbate quantum mechanical and quasi-classical methods are used to calculate the reaction cross section and product state distributions. A reaction cross section of 2–3 Å2 is found. Steering of the incident H atom towards the adsorbed Cl plays an important role in this large cross section. The product state distribution of the HCl has over an eV in vibrational energy and less than one eV in each of the translational and rotational distributions. Reactivity at impact parameters less than 1.0 Å is found to be dependent on the incident energy and vibrational state of the adsorbate. Single adsorbate corrugated surface studies show an increase in reactivity at small impact parameters. Using multiadsorbate quasi-classical methods and a corrugated potential energy surface, we have found that H atoms react with Cl atoms adsorbed onto a Au(111) surface to produce HCl via Eley-Rideal (ER), Hot Atom (HA), and Langmuir-Hinschelwood (LH) pathways. We observe two ER mechanisms. At small normal incidence energies, reaction results from a more-or-less direct collision with the Cl, leading to a large amount of product vibration, and relatively cold rotation and translation. In the second mechanism, more dominant at near-normal incidence and/or large incident energies, the H atom passes near the Cl, recoils from the metal, and is pulled into orbit about the Cl. This leads to broader product state distributions, and a more even distribution of the 3.0 eV of available energy among the product degrees of freedom, similar to products formed via the HA pathway. Overall, ER processes tend to contribute less than 10% to the reactivity, and most of the HCl is formed via HA processes. There is an increase in HCl formation with surface temperature for both the ER and HA mechanisms, but this increase is relatively weak. We observe typically about 12% H atom sticking, which would lead to HCl formation via a LH process in the experiments, above 140 K. We observe a weak forward scattering due to the direct ER component, as in the experiments. However, unlike the experiments, we observe a dip in our product angular distributions about &thetas;f = 0°, which we ascribe to our quasi-classical approximation. While we tend to see more energy in the hot products than in the experiments, our product translational, rotational, and vibrational distributions are in relatively reasonable agreement with those measured. One major disagreement with experiment is that there is apparently a significant sticking of the H atom at low temperatures, leading to a large LH component. In addition, the ER and HA components increase much more strongly with temperature than in the calculations. It is possible that electon-hole pair excitations in the metal strongly relax both the H atom and the excited HCl molecules formed.^ Part II. A quantum mechanical method is presented for studying the dynamics of the dissociative chemisorption of methane on metal surfaces. An oscillating transition state barrier that incorporates electronic effects is introduced. The minimum energy path for the dissociative chemisorption of CH4 on a Ni(111) surface is presented. Two scenarios are considered. The first includes the surface in its minimum energy geometry. The second looks at the effect on the transition state barrier when a Ni atom is moved 0.2 Å above the surface plane. The transition state barrier's height and width are found to decrease when the Ni atom at which the reaction occurs is perturbed from its equilibrium geometry.^

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Growing global energy demands have necessitated the search for alternative sources of renewable fuels. Dye-sensitized photocatalysis (DSP) is a promising low cost, sustainable method that directly converts solar energy to readily usable forms of energy such as hydrogen fuel. While DSP is a promising technology, its efficiency is limited by back electron transfer and kinetic redundancy. In order to fully understand these processes, single-molecule spectroscopy (SMS) is used to probe the electron transfer (ET) dynamics of photosensitizers. In particular, eosin Y (EY), a brominated fluorescein derivative that undergoes intersystem crossing prior to injection, is investigated using SMS. In this approach, blinking dynamics - stochastic fluctuations in emissive and nonemissive intensities under continuous photoexcitation - are measured for single molecules of EY on glass, TiO2, and in oxic and anoxic environments. The emission dynamics are parsed into emissive (“on”) and nonemissive (“off”) events and fit to cumulative probability distributions using a maximum likelihood estimation and Kolmogorov-Smirnov test approach. In the absence of TiO2, the data are lognormally distributed, consistent with triplet state decay and dispersive electron transfer. However, for EY-sensitized TiO2, the on- and off-time distributions are not well described by any tested functional form, motivating us to implement new modeling approaches (e.g., finite mixture model, Monte Carlo simulations). Our results show that back-to-back events, temporal binning, and thresholding obscure the functional form and are thus important considerations for understanding the underlying ET dynamics.

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