This review concerns light-to-chemical energy conversion, focusing on approaches that could be driven by terrestrial sunlight to produce hydrogen and/or reduce carbon dioxide. Recent advances in photocatalytic (PC) and photoelectrocatalytic (PEC) materials are covered. In both approaches, the electron-hole pairs that are created by photon absorption must travel in specific directions to the sites that mediate multielectron bond making/breaking redox reactions. Thermodynamic requirements for materials stability are described, although some recently discovered materials appear to be exceptions. For PC materials, the importance of rate matching between reduction and oxidation processes and the mass transfer of intermediates and products is emphasized. Surprisingly, metal sulfides appear to be promising for PC carbon dioxide reduction. For PEC materials, recent work elucidating the elementary step mechanism for oxygen evolution on metal oxides and the discovery of chalcogen-based photocathode materials capable of sustained light-driven CO2 reduction are discussed.

Recent advancements in transmission electron microscopy (TEM) have substantially expanded our capability to observe nanocrystals at unprecedented spatial and temporal resolutions. Innovations in TEM instruments, specimen preparation, and imaging modality have overcome historical limitations related to radiation damage, weak contrast for light elements, 2D projection limitations, and high-vacuum constraints. Additionally, advanced image processing techniques, particularly those incorporating machine learning, have enhanced data interpretation by enabling denoising, segmentation, and quantitative analysis. These advancements now enable the atomic-scale visualization of structural motifs, defects, strain distributions, and dynamic structural transformations of nanocrystals in realistic environments, including liquids and gases. The integration of these emerging TEM techniques promises novel insights into nanoscale processes that directly link atomic structure and dynamics to functional properties, thus significantly advancing the ultimate goal of materials by design.

Complex spatiotemporal correlations direct heterogeneous reactions spanning from the atomic- to meso-length scales with illustrations ranging from single-molecule adsorption to the oxidation of graphitic materials. Capturing the on-surface dynamics that underpin such processes benefits from spatially resolved and real-time in situ characterization of surface morphologies and adsorbed species, especially when paired with molecular scattering systems that provide tight control of incident molecular energy and approach geometry. Direct visualization shows that site-specific reactivity, correlated surface fluctuations, and structurally dependent reaction rates are interrelated to the on-surface fate of scattered species. Recent advances in neutral helium atom scattering are also presented as pathways for elucidating surface electron-phonon coupling dynamics. Overall, experiments presented herein represent a new direction for the interrogation of on-surface dynamics in which incident kinematics and energetics are tunable control parameters that influence time-evolving surface dynamics-and provide an incisive complement to traditional scattering experiments that monitor volatile products and scattered species.

Ultrafast core-to-valence transient absorption spectroscopy has emerged as a powerful technique for monitoring nonequilibrium chemical dynamics with element and site specificity. Owing to advancements in the robust, tabletop generation of ultrafast extreme ultraviolet (XUV) and soft X-ray (SXR) pulses, this technique has been applied to great effect in investigating electronic excited-state dynamics in various gas-phase molecules. This review begins with an overview of the experimental advances that have enabled laboratory-scale XUV and SXR production with particular emphasis on high-harmonic generation, central to modern implementations of tabletop core-to-valence transient absorption spectroscopy. We then highlight a collection of landmark studies that demonstrate the unprecedented insights this technique yields into the site-specific excited-state dynamics governing photoinduced processes such as bond dissociation, conformational change, and electronic relaxation in gas-phase molecules. We conclude with an outlook on future frontiers, including control of excited-state dynamics, other nonlinear X-ray spectroscopies, and next-generation light sources.

Actinides are inherently unstable and undergo nuclear decay processes with a concurrent release of energy. Consequently, they are used for nuclear power generation, nuclear weapons, and nuclear medicine. However, the radioactive decay processes also pose significant technological problems for the safe treatment and storage of spent nuclear materials. Cost-effective extraction of the actinides is the key first step in the remediation of nuclear waste, but the appropriate chemical means have yet to be determined. Our present understanding of the chemistry of actinides is limited, with the role of the 5f electrons posing a set of particularly challenging questions. The work reported here is focused on the use of electronic spectroscopy to probe the bonding of small molecules in the gas phase that contains thorium or uranium. Analyses of these data, carried out within the framework of ligand field theory, reveal clear evidence that the 5f electrons are spectators that retain their atomic metal ion character.

Dynamics of molecular interactions with solid surfaces, such as scattering, adsorption/desorption, diffusion, and reaction, are affected by energy dissipation at surfaces. Recent progress in experimental studies of surface dynamics has stimulated intense interest in theoretical investigation of microscopic mechanisms and pathways of energy transfer. This review summarizes recent developments in modeling such processes, emphasizing new understandings of electronically adiabatic and nonadiabatic energy dissipation mechanisms and dynamics in representative systems, using various theoretical methods. In particular, machine learning has been leveraged to represent high-dimensional adiabatic potential energy surfaces, electronic friction tensors, and effective multielectron diabatic Hamiltonians. When integrated with mixed quantum-classical dynamics methods, such as molecular dynamics with electronic friction and independent electron surface hopping, these first-principles-based simulations provided unprecedented insights into the roles played by adiabatic and nonadiabatic energy dissipation channels in surface dynamics and in-depth interpretation of experimental observations.

In my undergraduate studies at the Massachusetts Institute of Technology (MIT), the short-lived chemical physics major allowed me to evade a number of courses required for chemistry majors. Thus, it was possible to take many physics courses and most of the advanced PhD-level courses in physical chemistry. I also took the introductory electrical engineering course in computer programming. The latter allowed me to write lots of computer code as a part of my (passing, but largely unsuccessful) senior thesis directed graciously by Professor Walter Thorson. As recommended by MIT Professor John C. Slater, I moved to Stanford University with Professor Frank Harris as my PhD supervisor. Frank was the perfect advisor for me, providing very close direction during the first year, and then allowing me to develop more and more independently. Within a few days of my twenty-fifth birthday, I became an assistant professor of chemistry at the University of California, Berkeley. Eighteen years later, I moved to the University of Georgia as director of a new research institute.

Hydrated electrons are created in virtually every radiation environment and in many photochemical or electrochemical environments where liquid water is present, so their reaction products and reaction rate constants are naturally important in applications. Thanks to the strong optical absorbance of (e-)aq, these rate constants are easy to measure, and a large database has been accumulated. It is not generally appreciated that no working theory of hydrated electron reaction rates presently exists. We discuss key experimental observations of hydrated electron reactions in the context of recent progress in theoretical and simulation developments toward understanding them, made possible by ever increasing computational power.

The oxidation of gas-phase SO2 to sulfate aerosols has been a driver of urban air pollution since the Great Smog of London in 1952. Traditionally, this reaction has been perceived as a quintessential atmospheric aqueous reaction, occurring within condensed water such as cloud and fog droplets. This established view has been challenged by recent studies showing that, in urban air pollution, sulfate aerosols form predominantly through a heterogeneous SO2 conversion at aerosol surfaces. This review summarizes recent advances in understanding this heterogeneous process, focusing on (a) why S(IV) oxidation is faster at the air-water interface, (b) how to experimentally determine the reaction location with the scaling relationships of apparent reaction kinetics, and (c) how to predict, or retrieve, the localized surface reaction kinetics with multiscale models. We conclude by discussing open questions and remaining challenges, with the central theme of how the interfacial heterogeneous process may redefine our understanding of atmospheric sulfur chemistry.

Vibrational spectroscopy and fluorescence spectroscopy have historically been two established but separate fields of molecular spectroscopy. While vibrational spectroscopy provides exquisite chemical information, fluorescence spectroscopy often offers orders of magnitude higher detection sensitivity. However, they each lack the advantages of each other. In recent years, a series of novel nonlinear optical spectroscopy studies have been developed that merge both spectroscopies into a single double-resonance process. These techniques combine the chemical specificity of Raman or infrared (IR) spectroscopy with the superb detection sensitivity and spatial resolution of fluorescence microscopy. Many facets have been explored, including Raman transition versus IR transition, time domain versus frequency domain, and spectroscopy versus microscopy. Notably, single-molecule vibrational spectroscopy has been achieved at room temperature without the need for plasmonics. Even superresolution vibrational imaging beyond the diffraction limit was demonstrated. This review summarizes the growing field of vibrational-encoded fluorescence microscopy, including key technical developments, emerging applications, and future prospects.