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.

In this review, we survey the use of extreme ultraviolet absorption spectroscopy to measure electronic and vibrational dynamics in transition metal complexes. Photons in this 30-100 eV energy range probe 3p → 3d transitions for 3d metals and 4f, 5p → 5d transitions in 5d metals, and the resulting spectra are sensitive to the spin state, oxidation state, and ligand field of the metal. Furthermore, the energy of the core level depends on the metal, providing elemental specificity. Use of tabletop high-harmonic sources allows these spectra to be measured with femtosecond to attosecond time resolution in a standard laser laboratory, revealing short-lived states in chromophores and photocatalysts that were unresolved using other techniques.

The C60 fullerene molecule has been the subject of intense study for four decades, starting with its identification in the mass spectra of carbon soot in 1985. In this review, we focus on the achievement of ultra-high-resolution spectroscopy of gas phase neutral C60, heralded by the observation of quantum state-resolved infrared spectra in 2019. C60 is now the largest and most symmetric molecule for which rovibrational quantum state resolution has been achieved, motivating the use of large molecules for studying complex quantum systems with symmetries and degrees of freedom not readily available in other composite systems. We discuss the theory, challenges, and experimental techniques of high-resolution C60 spectroscopy and recent experimental results probing the structure, dynamics, and interactions of C60 enabled by quantum state resolution.

How long thread-like eukaryotic chromosomes fit tidily in the small volume of the nucleus without significant entanglement is just beginning to be understood, thanks to major advances in experimental techniques. Several polymer models, which reproduce contact maps that measure the probabilities that two loci are in spatial contact, have predicted the 3D structures of interphase chromosomes. Data-driven approaches, using contact maps as input, predict that mitotic helical chromosomes are characterized by a switch in handedness, referred to as perversion. By using experimentally derived effective interactions between chromatin loci in simulations, structures of conventional and inverted nuclei have been accurately predicted. Polymer theory and simulations show that the dynamics of individual loci in chromatin exhibit subdiffusive behavior but the diffusion exponents are broadly distributed, which accords well with experiments. Although coarse-grained models are successful, many challenging problems remain, which require the creation of new experimental and computational tools to understand genome biology.

Information is an important resource. Storing and retrieving information faithfully are huge challenges and many methods have been developed to understand the principles behind robust information processing. In this review, we focus on information storage and retrieval from the perspective of energetics, dynamics, and statistical mechanics. We first review the Hopfield model of associative memory, the classic energy-based model of memory. We then discuss generalizations and physical realizations of the Hopfield model. Finally, we highlight connections to energy-based neural networks used in deep learning. We hope this review inspires new directions along the lines of information storage and retrieval in physical systems.

The optical centrifuge was demonstrated in 2000 as a tool for preparing ensembles of molecules in extreme rotational states. Highly rotationally excited molecules, so-called superrotors, are observed as products of photodissociation and molecular collisions, in high-temperature environments in the atmospheres of Earth and exoplanets, and in the interstellar medium. Traditional optical excitation is limited to small changes in rotation, limiting experiments to relatively low rotational states. In this review, I discuss the use of a tunable optical centrifuge to prepare molecules in selected ranges of excited rotational states and investigations of their collisional relaxation using state-resolved polarization-sensitive transient IR probing. I examine the decay dynamics of population, alignment, and translational energy release, focusing on experimental results, and compare them with simulations that overestimate observed relaxation rates. A clear picture of near-resonant and nonresonant energy transfer pathways emerges and establishes the means to distinguish superrotor and bath collision products.