Femtochemistry: Atomic‐Scale Dynamics of the Chemical Bond Using Ultrafast Lasers (Nobel Lecture)
TL;DR: The femtosecond resolution (1 fs = 10^(−15) s) is the ultimate achievement for studies of the fundamental dynamics of the chemical bond as discussed by the authors, which is the wellspring of the field of femtochemistry.
Abstract: Over many millennia, humankind has thought to explore phenomena on an ever shorter time scale. In this race against time, femtosecond resolution (1 fs=10^(−15) s) is the ultimate achievement for studies of the fundamental dynamics of the chemical bond. Observation of the very act that brings about chemistry—the making and breaking of bonds on their actual time and length scales—is the wellspring of the field of femtochemistry, which is the study of molecular motions in the hitherto unobserved ephemeral transition states of physical, chemical, and biological changes. For molecular dynamics, achieving this atomic-scale resolution using ultrafast lasers as strobes is a triumph, just as X-ray and electron diffraction, and, more recently, STM and NMR spectroscopy, provided that resolution for static molecular structures. On the femtosecond time scale, matter wave packets (particle-type) can be created and their coherent evolution as a single-molecule trajectory can be observed. The field began with simple systems of a few atoms and has reached the realm of the very complex in isolated, mesoscopic, and condensed phases, as well as in biological systems such as proteins and DNA structures. It also offers new possibilities for the control of reactivity and for structural femtochemistry and femtobiology. This anthology gives an overview of the development of the field from a personal perspective, encompassing our research at Caltech and focusing on the evolution of techniques, concepts, and new discoveries.
Citations
More filters
TL;DR: The method has the sensitivity to measure a 0.1 Å displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.
Abstract: Molecular structures are imaged with sub-angstrom precision and exposure times of a few femtoseconds. Molecular imaging, or the determination of the positions of atoms in molecules, is an important technique in the physical, chemical and biological sciences. But going beyond mere structure determination, recent technical developments offer the tantalizing prospect of access to ultrafast snapshots of biological molecules and condensed-phase systems undergoing structural changes. One approach uses laser-ionized bursts of coherent electron wave packets to self-interrogate the parent molecular structure. Here, Blaga et al. use this laser-induced electron diffraction (LIED) method to map the structural responses of oxygen and nitrogen molecules to ionization. By measuring a 0.1-angstrom displacement in the oxygen bond length occurring in a time interval of about 5 femtoseconds, the authors establish LIED as a promising approach for imaging of gas-phase molecules with unprecedented spatio-temporal resolution. Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-angstrom spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules1,2 and condensed-phase systems3,4,5,6 undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure7,8,9,10,11. Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction10 (LIED), to image molecular structures with sub-angstrom precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3 μm) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1 A displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.
498 citations
TL;DR: In this paper, results mostly from the last two decades of research on this subject are summarized, obtained either from infrared spectroscopy with a resolution of as high as cm or, in a different approach, by using various pump-probe schemes with a temporal resolution from dozens of picoseconds to subpicosecond.
Abstract: Intramolecular vibrational redistribution is a fundamental phenomenon observed in polyatomic molecules when sufficiently excited vibrationally. In this paper, results mostly from the last two decades of research on this subject are summarized, obtained either from infrared spectroscopy with a resolution of as high as cm or, in a different approach, by using various pump-probe schemes with a temporal resolution from dozens of picoseconds to subpicoseconds.
428 citations
19 Jul 2019
TL;DR: In this paper, the authors summarized the up-to-date progress in the studies of carbon materials, and emphasized on the combination of experiment and theory to clarify the underlying mechanisms of these materials.
Abstract: The sluggish kinetics of Oxygen Reduction Reaction (ORR) at the cathode in proton exchange membrane fuel cells or metal-air batteries requires highly effective and stable electrocatalysts to boost the reaction. The low abundance and high price of Pt-based electrocatalysts hamper the widespread application of proton exchange membrane fuel cells and metal-air batteries. As promising alternatives, metal-free carbon materials, especially upon doping heteroatoms or creating defects demonstrated excellent ORR activity, which is as efficient as or even superior to commercial platinum on carbon. Significant progress on the development of advanced carbon materials as highly stable and durable catalysts has been achieved, but the catalytic mechanisms of these materials still remain undistinguished. In present review, we summarized the up-to-date progress in the studies of carbon materials, and emphasized on the combination of experiment and theory to clarify the underlying mechanisms of these materials. At last, we proposed the perspectives on the proper strategies of elucidating the mechanisms of carbon materials as electrocatalysts towards ORR.
426 citations
TL;DR: The design, self-assembly, and applications of polyfunctional supramolecules incorporating functional moieties with host-guest, photonic, materials, and self-organizational properties is discussed.
310 citations
TL;DR: The present review presents the first comprehensive report of current knowledge (including synthesis aspects not discussed before) regarding the related giant metal-oxide clusters mainly of the type {Mo(57)M'(6)} (M' = Fe(III), V(IV)) (torus structure),
Abstract: Following Nature's lessons, today chemists can cross the boundary of the small molecule world to construct multifunctional and highly complex molecular nano-objects up to protein size and even cell-like nanosystems showing responsive sensing. Impressive examples emerge from studies of the solutions of some oxoanions of the early transition metals especially under reducing conditions which enable the controlled linking of metal-oxide building blocks. The latter are available from constitutional dynamic libraries, thus providing the option to generate multifunctional unique nanoscale molecular systems with exquisite architectures, which even opens the way towards adaptive and evolutive (Darwinian) chemistry. The present review presents the first comprehensive report of current knowledge (including synthesis aspects not discussed before) regarding the related giant metal-oxide clusters mainly of the type {Mo57M′6} (M′ = FeIII, VIV) (torus structure), {M72M′30} (M = Mo, M′ = VIV, CrIII, FeIII, MoV), {M72Mo60} (M = Mo, W) (Keplerates), {Mo154}, {Mo176}, {Mo248} (“big wheels”), and {Mo368} (“blue lemon”) – all having the important transferable pentagonal {(M)M5} groups in common. These discoveries expanded the frontiers of inorganic chemistry to the mesoscopic world, while there is probably no collection of discrete inorganic compounds which offers such a versatile chemistry and the option to study new phenomena of interdisciplinary interest. The variety of different properties of the sphere- and wheel-type metal-oxide-based clusters can directly be related to their unique architectures: The spherical Keplerate-type capsules having 20 crown-ether-type pores and tunable internal functionalities allow the investigation of confined matter as well as that of sphere-surface-supramolecular and encapsulation chemistry – including related new aspects of the biologically important hydrophobic effects – but also of nanoscale ion transport and separation. The wheel-type molybdenum-oxide clusters exhibiting complex landscapes do not only have well-defined reaction sites but also show unprecedented adaptability regarding the integration of various kinds of matter. Applications in different fields, e.g. in materials science and catalysis including those in small spaces, investigated by several groups, are discussed while possible directions for future work are outlined.
303 citations
References
More filters
TL;DR: This anthology gives an overview of the development of the field of femtochemistry from a personal perspective, encompassing the research at Caltech and focusing on the evolution of techniques, concepts, and new discoveries.
Abstract: Over many millennia, humankind has thought to explore phenomena on an ever shorter time scale. In this race against time, femtosecond resolution (1 fs=10^(−15) s) is the ultimate achievement for studies of the fundamental dynamics of the chemical bond. Observation of the very act that brings about chemistry—the making and breaking of bonds on their actual time and length scales—is the wellspring of the field of femtochemistry, which is the study of molecular motions in the hitherto unobserved ephemeral transition states of physical, chemical, and biological changes. For molecular dynamics, achieving this atomic-scale resolution using ultrafast lasers as strobes is a triumph, just as X-ray and electron diffraction, and, more recently, STM and NMR spectroscopy, provided that resolution for static molecular structures. On the femtosecond time scale, matter wave packets (particle-type) can be created and their coherent evolution as a single-molecule trajectory can be observed. The field began with simple systems of a few atoms and has reached the realm of the very complex in isolated, mesoscopic, and condensed phases, as well as in biological systems such as proteins and DNA structures. It also offers new possibilities for the control of reactivity and for structural femtochemistry and femtobiology. This anthology gives an overview of the development of the field from a personal perspective, encompassing our research at Caltech and focusing on the evolution of techniques, concepts, and new discoveries.
436 citations