We present a calculation of vibrational frequencies of formate on the AuPt(111) surface alloy including full anharmonicity and coupling of all six intramolecular degrees of freedom. This species is a key intermediate in methanol oxidation on this material. We use a modified version of the method of Manzhos and Carrington to compute the spectrum directly from a small number (<10,000) of DFT single-point energies, bypassing the construction of a potential energy surface. This is the first such calculation for a 4-atomic species at a surface. The spectrum is obtained using rectangular collocation and a small basis set of parameterized Hermite functions. The achievable accuracy of the order of several cm-1 corresponds to the typical experimental resolution. Using normal coordinates makes the equations simple and general and easily applicable to other systems. This calculation is doable on a PC. We predict that anharmonicity and coupling lower the fundamental frequencies by dozens of cm-1, which could affect species assignment.

Metallic quantum clusters are stable structures that can exhibit many useful properties. Clusters can be ligand stabilized in aqueous environments to expand their usefulness as biosensors. There are some limitations in characterizing the physical and chemical properties of individual water soluble clusters. This report describes initial results of a new approach for detecting and characterizing individual gold nanoclusters (Au25(SG)18) in an aqueous solution with nanopore-based resistive pulse sensing. Here the nanopore is a single alpha hemolysin from Staphylococcus aureus. Clusters that enter through the cis side of the pore (large vestibule) usually create shallow current blockades with a mean residence time of several milliseconds. Clusters that enter through the trans side of the pore (narrow lumen) create deeper blockades that are either very short (∼200 μs), long lived (∼50 ms) or trapped (>10s). The short and long lived blockades yield sufficient statistics to help characterize the clusters and the trapped state events may allow for additional analysis and controlled delivery of individual clusters. We demonstrate the possibility of this additional analysis by performing I-V measurements on individually trapped clusters. These show an optimal voltage for confining a cluster within the pore.

Recently, the usage of optical fiber coils has increased significantly, especially in the design of physic and chemical sensors. Therefore, it is important to test the theoretical current models developed to predict the power loss throughout optical fiber. In this paper a pioneer and popular model, the Marcuse model of power loss, was studied and evaluated for optical fiber coils of small radii. Power attenuation in a bent fiber data was collected using an Optical Time Domain Reflectometer (OTDR), and it was compared to the theoretical predictions of the Marcuse model. It was observed that the model predicts correctly the attenuation behavior for usual curvature radii, however, it fails to predict accurately the attenuation behavior for small curvature radii, underestimating considerably the actual power loss. Also, it has been observed that at small radii the power loss parameter 2α and the mode propagation constant of the wave guide β stop being constants and become functions of the optical path, particularly of the number of loops in the coil. It is possible that new mechanisms of light leaking are present, due to the extreme distortion of the modes configuration into the fiber at small radii. Those mechanisms cannot be described by a model that considers a power loss parameter 2α, and more specifically the mode propagation constant of the wave guide (β) as constants. Then it is important to develop other models where the previous parameters can be considered as functions of the optical path.