Ultrafast Molecular Reaction Dynamics in Real-Time: Progress Over a Decade

Khundkar, Lutfur R.; Zewail, Ahmed H.

doi:10.1146/annurev.pc.41.100190.000311

Cited by 317 publications

(124 citation statements)

References 67 publications

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“…One could think that such experiments should be performed for atoms, but how this would be done is not necessarily obvious. Molecules going through conical intersections and other narrow bottlenecks show a remarkable retention of their phases (19,(26)(27)(28)(29)(30). Then the pump (or probe) can also be tailored up to and including interference between the pump (or probe) pulses.…”

Section: Discussionmentioning

confidence: 99%

A molecular logic gate

Kompa

Levine

2001

Proc. Natl. Acad. Sci. U.S.A.

132

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We propose a scheme for molecule-based information processing by combining well-studied spectroscopic techniques and recent results from chemical dynamics. Specifically it is discussed how optical transitions in single molecules can be used to rapidly perform classical (Boolean) logical operations. In the proposed way, a restricted number of states in a single molecule can act as a logical gate equivalent to at least two switches. It is argued that the four-level scheme can also be used to produce gain, because it allows an inversion, and not only a switching ability. The proposed scheme is quantum mechanical in that it takes advantage of the discrete nature of the energy levels but, we here discuss the temporal evolution, with the use of the populations only. On a longer time range we suggest that the same scheme could be extended to perform quantum logic, and a tentative suggestion, based on an available experiment, is discussed. We believe that the pumping can provide a partial proof of principle, although this and similar experiments were not interpreted thus far in our terms. The need for increasing miniaturization of logical circuits is foreseen to soon reach the physical limit of MOSFET (Metal Oxide Semiconductor Field Effect) Transistors. There is therefore a worldwide search for alternatives. Single-molecule-based switches (1, 2) rectifiers (3, 4), and wires (5) Other important recent work in this direction is reviewed in refs. 6 and 7. A different route, which has been studied for some time (8-10), is to combine chemical inputs with optical outputs. These are typically solution phase experiments, which have used to advantage the progress in supramolecular chemistry for the construction of molecular machines (11,12).We discuss a molecule-based scheme for logical operations, which is different in its features. One merit of our scheme is that it involves well-established and well-characterized photophysicochemical processes. This enables us to know that we could anticipate eventually an ultrafast processing and can expect a rather fast (picosecond time scale) response, even in preliminary studies. A point of chemical importance is that the scheme operates with the kind of molecules for which one has a great scope for organic synthesis so as to tailor the molecule to specific responses, both optical and kinetic. An important limitation, common to our scheme and to other proposals for computing with molecules (7), is the challenge of connecting the molecules. This paper provides an introduction to our proposal for molecular information processing, stressing the fundamental issues and avoiding mathematical formalism.In the background to our discussion is the observation by Shannon (13) that there is an analogy between switches and Boolean logic operations. In fact, Shannon's proposal predates the invention of transistors and was first applied to electromechanical switches. The point is that it takes at least two switches to represent a logic operation. Fig. 1 shows a schematic representation of circuits tha...

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Section: Discussionmentioning

confidence: 99%

A molecular logic gate

Kompa

Levine

2001

Proc. Natl. Acad. Sci. U.S.A.

132

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“…It promises to be a revolutionary way to increase reaction efficiencies and enhance the reaction products. Crossed molecular beam experiments at femto-scale [57] to atto-scale [58,59] use ultrafast pulsed lasers which permit the monitoring of the reacting molecular species on a sub-picosecond scale; then, reaction mechanisms can then be inferred from the details of the dynamics as the reaction proceeds from reactants to products. In addition, in the last few years, it has become possible to image chemical reactivity at the single-molecule and-particle level with fluorescence microscopy; however in order to image a chemical process, it needs to be associated with a change in fluorescent output that is detectable.…”

Section: Chemical Structure (Bond) and Reactivitymentioning

confidence: 99%

Chemical structure and reactivity by means of quantum chemical topology analysis

Andrés

González-Navarrete

Safont

2015

Computational and Theoretical Chemistry

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Chemical structure and bonding are key features and concepts in chemical systems which are used in deriving structure-property relationships, and hence in predicting physical and chemical properties of compounds. Even though the contemporary high standards in determination, using both theoretical methods and experimental techniques, questions of chemical bonds as well as their evolution along a reaction pathway are still highly controversial. This paper presents a working methodology to determine the structure and chemical reactivity based on the quantum chemical topology analysis.QTAIM and ELF frameworks, based on the topological analysis of the electron density and the electron localization function, respectively, have been used. We have selected two examples studied by the present approach, to show its potential: (i) QTAIM study on the α -Ag 2 WO 4 , for the simulation of Ag nucleation and formation on α -Ag 2 WO 4 provoked in this crystal by the electron-beam irradiation. (ii) An ELF and Thom´s catastrophe theory study for the reaction pathway associated with the decomposition of stable planar hypercoordinate carbon species, CN 3 Mg 3 + .3Chemistry is the science of substances: their structure, their properties, and the reactions that change them into other substances, as Linus These procedures are hugely successful and they can be considered as an energeticsdriven approach to computational theoretical and chemistry. Then, this research field constitutes a central application of quantum chemistry to the study of stationary points of PESs [53] and the pathways connecting them. The shape of an adiabatic PES is conventionally regarded as a function of the nuclear skeleton, ignoring the wealth of information that can be provided by the total electronic charge density distribution ρ(r).The driving force for the nuclear motion is the potential, which arises from In this context, the electronic structure of a molecule is described in real space terms using topological analysis. Beyond the well-known approach of the QTAIM, which relies on the properties of the electron density ρ(r) when atoms interact, topological analysis of different scalar functions can be employed, such as the electron localization function (ELF) method [90][91][92][93]. Originally, ELF can be developed based on the conditional pair density [90] or can be derived from the kinetic energy density [94].In the latter context, ELF is seen as the scaled difference between the positive kinetic energy density and the von Weizsäcker term [95], whereby the scaling function is the 8 kinetic energy density of the homogeneous electron gas (Thomas-Fermi term) [96,97]. The pictures of a molecule as drawn by the QTAIM and ELF analysis are complementary. Thus, the QTAIM analysis is based on the topology of the electron density ρ(r), whereas the ELF analysis is based on the topology of the electron localization function using the conditional probability for the same spin pairs which is closely related to the local excess of kinetic energy due to the Paul...

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“…The time evolution of the induced coherences has been studied either by measuring the total fluorescence emitted from excited electronic states [1] or by ionizing the moleeule and measuring the transient ionization spectrum as a function of the pump-probe time delay [2]. Molecular vibrational wave packet motion has been observed for a number of systems.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond Dynamics of Molecular and Cluster Ionization and Fragmentation

Baumert¹,

Thalweiser²,

Weiß³

et al. 1993

Ultrafast Phenomena VIII

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Abstract. The real-time dynamics of molecular CNa 2 . Na 3) and cluster Na n Cn=4-2D multiphoton ionization and -fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Wave packet motion in the dimer Na 2 reveals two independent multiphoton ionization processes while the higher dimensional motion in the trimer Na 3 reflects the chaotic vibrational motion in this floppy system. The first studies of cluster properties C energy I bandwidth and lifetime of intermediate resonances Na~) wi th femtosecond laser pulses give a striking illustration of the transition from "rnolecule-like" excitations to "surfaceplasrna-like resonances for increasing cluster sizes. Time-resolved fragmentation of cluster ions Na~indicate that direct photo-induced fragmentation processes are more important at short times than the statistical unimolecular decay.

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Ultrafast Molecular Reaction Dynamics in Real-Time: Progress Over a Decade

Cited by 317 publications

References 67 publications

A molecular logic gate

A molecular logic gate

Chemical structure and reactivity by means of quantum chemical topology analysis

Femtosecond Dynamics of Molecular and Cluster Ionization and Fragmentation

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