Infrared spectra of tropolone(OH) and tropolone(OD) obtained from vapor phase, solvated, and rare gas matrix-isolated samples, and from fluorescence dip infrared spectroscopy experiments by Frost et al. on jet-cooled samples, are analyzed with the guidance of high level ab initio molecular orbital (MO) computations. It is found that the anharmonicity of the double minimum global potential energy surface of S0 tropolone is manifested by multistate local resonance networks coupling fundamental vibrations to nearby overtone and combination states. These resonance networks pervade the IR spectrum of tropolone above 500 cm−1, and the absorbances are much more strongly perturbed from harmonic level predictions than the frequencies. Some of the IR absorbances are also sensitive to intermolecular interactions. At maximum spectral resolutions reaching ∼0.2 cm−1 only the v1 and v22 (OH stretching and nascent skeletal tunneling) vibrations show resolved vibrational state-specific tunneling doublets. The tunneling behavior of tropolone is analyzed in the accompanying article.

This report introduces a type of plasmonic crystal that consists of metal coated nanostructures of relief molded on a polymer film as a substrate for surface-enhanced Raman scattering ͑SERS͒. Such crystals exhibit SERS enhancement factors of ϳ10 5 , over large areas and with sufficiently high levels of uniformity for precise two-dimensional Raman mapping of surface bound monolayers. The ease of fabrication together with the high sensitivities and spatial resolution that can be achieved suggests an attractive route to SERS substrates for portable chemical warfare agent detection, environmental monitors, noninvasive imaging of biomolecules, and other applications.

FeMoco, MoFeSC, has been shown to be the active catalytic site for the reduction of nitrogen to ammonia in the nitrogenase protein. An understanding of its electronic structure including strong electron correlation is key to designing mimic catalysts capable of ambient nitrogen fixation. Active spaces ranging from [54, 54] to [65, 57] have been predicted for a quantitative description of FeMoco's electronic structure. However, a wave function approach for a singlet state using a [54, 54] active space would require 10 variables. In this work, we systematically explore the active-space size necessary to qualitatively capture strong correlation in FeMoco and two related moieties, MoFeS and FeS. Using CASSCF and 2-RDM methods, we consider active-space sizes up to [14, 14] and [30, 30], respectively, with STO-3G, 3-21G, and DZP basis sets and use fractional natural-orbital occupation numbers to assess the level of multireference electron correlation, an examination of which reveals a competition between single-reference and multireference solutions to the electronic Schrödinger equation for smaller active spaces and a consistent multireference solution for larger active spaces.

Metallic nanostructures such as systems containing metal nanoparticles or nanostructured metal films are intriguing systems of much current interest. Surface plasmons, i.e., special electronic excitations near the metallic surfaces, can then be excited in these systems. Surface plasmons can be intense and localized, and correctly describing their behavior in complex systems can require numerically rigorous modeling techniques. The finite-difference time-domain (FDTD) method is one such technique. This review discusses results obtained mostly with the FDTD method concerning (i) local surface plasmon excitations of metal nanoparticles, (ii) surface plasmon polariton propagation on layered structures, (ii) and periodic hole arrays in metal films.

Three-dimensional finite-difference time-domain simulations were performed to explore the excitation of surface plasmon resonances in long silver (Ag) nanowires. In particular, we show that it is possible to generate plasmonic wave packets that can propagate along the nanowire by exciting superpositions of surface plasmon resonances. By using an appropriately chirped pulse, it is possible to transiently achieve localization of the excitation at the distal end of the nanowire. Such designed coherent superpositions will allow realizing spatiotemporal control of plasmonic excitations for enhancing nonlinear responses in plasmonic "circuits".