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2014 | Buch

Molecular Quantum Dynamics

From Theory to Applications

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Über dieses Buch

This book focuses on current applications of molecular quantum dynamics. Examples from all main subjects in the field, presented by the internationally renowned experts, illustrate the importance of the domain. Recent success in helping to understand experimental observations in fields like heterogeneous catalysis, photochemistry, reactive scattering, optical spectroscopy, or femto- and attosecond chemistry and spectroscopy underline that nuclear quantum mechanical effects affect many areas of chemical and physical research. In contrast to standard quantum chemistry calculations, where the nuclei are treated classically, molecular quantum dynamics can cover quantum mechanical effects in their motion. Many examples, ranging from fundamental to applied problems, are known today that are impacted by nuclear quantum mechanical effects, including phenomena like tunneling, zero point energy effects, or non-adiabatic transitions. Being important to correctly understand many observations in chemical, organic and biological systems, or for the understanding of molecular spectroscopy, the range of applications covered in this book comprises broad areas of science: from astrophysics and the physics and chemistry of the atmosphere, over elementary processes in chemistry, to biological processes (such as the first steps of photosynthesis or vision). Nevertheless, many researchers refrain from entering this domain. The book "Molecular Quantum Dynamics" offers them an accessible introduction. Although the calculation of large systems still presents a challenge - despite the considerable power of modern computers - new strategies have been developed to extend the studies to systems of increasing size. Such strategies are presented after a brief overview of the historical background. Strong emphasis is put on an educational presentation of the fundamental concepts, so that the reader can inform himself about the most important concepts, like eigenstates, wave packets, quantum mechanical resonances, entanglement, etc. The chosen examples highlight that high-level experiments and theory need to work closely together. This book thus is a must-read both for researchers working experimentally or theoretically in the concerned fields, and generally for anyone interested in the exciting world of molecular quantum dynamics.

Inhaltsverzeichnis

Frontmatter
1. Introduction and Conceptual Background
Abstract
Molecular Quantum Dynamics, often called “Quantum Dynamics,” is the subfield of Theoretical Chemistry where both the electrons and the nuclei of a molecular system are treated with a quantum-mechanical approach. Molecular Quantum Dynamics can be seen as the encounter of Quantum Physics and Chemistry.
Fabien Gatti, Benjamin Lasorne
2. Elementary Molecule–Surface Scattering Processes Relevant to Heterogeneous Catalysis: Insights from Quantum Dynamics Calculations
Abstract
We show some examples of molecule/surface systems that have been recently described using quantum dynamics simulations, such as H2/metal surfaces and CH4/metal surfaces. Quantum simulations performed on these systems have yielded results in excellent agreement with independent experimental measurements. These simulations have allowed, for example, the analysis of the role of the internal degrees of freedom of the molecule, the interpretation of puzzling controversial experimental results, and the suggestion of novel experiments.
Cristina Díaz, Axel Gross, Bret Jackson, Geert-Jan Kroes
3. Tunneling in Unimolecular and Bimolecular Reactions
Abstract
Tunneling is an important quantum phenomenon in reaction dynamics. In this chapter, the effects of tunneling on photodissociation and reactive scattering are discussed using two prototypical examples. The first deals with a unimolecular decomposition reaction, namely the photodissociation of NH3 in its first (A) absorption band and the second is concerned with an important bimolecular reaction in combustion: HO + CO → H + CO2. In the former case, the lifetimes of low-lying vibrational resonances in the predissociative excited state are influenced by tunneling through a small barrier in the dissociation (N–H) coordinate, which is also responsible for a strong H/D isotope effect. The latter, on the other hand, is affected by tunneling through a tight barrier in the exit channel primarily along the H–O dissociation coordinate, which is manifested by the non-Arrhenius rate constant at low temperatures, kinetic isotope effects, and vibrational mode selectivity. In addition, the photodetachment of HOCO produces metastable HOCO species, the decomposition of which is dominated by deep tunneling to the H + CO2 products. Since both systems are influenced by multidimensional tunneling, an accurate characterization of the dynamics requires a quantum mechanical (QM) treatment, preferably with full dimensionality. In this chapter, we review the recent advances in understanding the effects of tunneling in these two reactive systems.
Hua Guo, Jianyi Ma, Jun Li
4. Reactive Scattering and Resonance
Abstract
In this chapter, recent developments of the quantum wave packet methods for calculating differential cross sections (DCSs) of tetra-atomic reaction, for calculating DCSs of triatomic reaction using wave packet method only with reactant Jacobi coordinates, for calculating and analyzing the reactive resonance wave functions, and for simulating and explaining experimental observables of a reactive scattering, are given. Applications to the F + H2 reaction, especially some fundamental understandings of its short-lived reactive resonances, the H + O2 reaction, the H2 + OH → H + H2O reaction, and the OH + CO → H + CO2 reaction are presented for illustration.
Zhigang Sun, Bin Zhao, Shu Liu, Dong-H. Zhang
5. Vibrational Spectroscopy and Molecular Dynamics
Abstract
Quantum dynamical simulations in full dimensionality play an essential role in the field of molecular dynamics. This is shown with the help of two examples: (1) the simulation of the infrared spectrum of the Zundel cation (H5O2 +) and (2) the investigation of the tunneling splitting in malonaldehyde (C3H4O2). For the Zundel cation, full, 15-dimensional dynamics calculations are presented for different isotopomers and experimental spectra are assigned to vibrational transitions. Furthermore, the internal proton transfer process within the Zundel cation is discussed. For malonaldehyde, full, 21-dimensional calculations of the ground state, the four lowest fundamentals, and their tunneling splittings are presented. The results are, along with assignments, compared to experimental data and findings of other researchers.
Oriol Vendrell, Markus Schröder, Hans-Dieter Meyer
6. Vibronic Coupling Effects in Spectroscopy and Non-adiabatic Transitions in Molecular Photodynamics
Abstract
A brief historic and systematic survey is given of our efforts to elucidate important features of the nuclear motion on interacting potential energy surfaces (PESs). Starting with our early work in 1977, a variety of small to medium-sized polyatomic molecules have been treated by quantum-dynamical methods. As the key topological feature signalling the effects in question, conical intersections of PESs have been established. The associated strong nonadiabatic coupling effects manifest themselves as diffuse (at low resolution) or irregular (at high resolution) spectral structures upon electronic transitions. The concomitant fs electronic population decay governs the photophysical and photochemical properties of these systems. Representative examples with 2–5 strongly coupled electronic states are given, and the quantum nature of the phenomena is emphasized.
Horst Köppel
7. Non-adiabatic Photochemistry: Ultrafast Electronic State Transitions and Nuclear Wavepacket Coherence
Abstract
Chemistry that takes place exclusively in the ground electronic state can be well described by a reaction path in which the reactants pass over a transition state to the products. After photoexcitation, a molecule is in an excited electronic state and new topographical features joining different states, known as conical intersections, also need to be considered to describe the time-evolution from reactants to products. These intersections are due to the coupling between electrons and nuclei. In addition to providing new pathways, they provide a quantum-mechanical phase to the system which means that to describe the nuclear motion properly methods are required that include the resulting quantum-mechanical coherences in the nuclear motion. In this chapter, we review the nature and topography of conical intersections and simulation methods that have been developed to describe a molecule passing through one. These range from the full solution of the time-dependent Schrödinger equation to approximate methods based on Newtonian mechanics. Using examples the advantages and disadvantages of each are discussed.
Benjamin Lasorne, Graham A. Worth, Michael A. Robb
8. The Interplay of Nuclear and Electron Wavepacket Motion in the Control of Molecular Processes: A Theoretical Perspective
Abstract
The concept of coherent control of molecular processes with light is introduced, sketching the way from single parameter to the multiparameter control in the time domain. Optimal control theory is by now a widespread and well-recognized method to solve a variety of control tasks ranging from chemical to physical applications. The underlying concepts and tools with their links to the experiment will be introduced with the focus on chemical reactions. As they include the motion of the nuclei, their time scale ranges from femtoseconds to picoseconds and longer and requires the solution of the time-dependent Schrödinger equation for the nuclear motion. Recent developments that enter the sub-femtosecond domain and open the prospect for direct control of the faster electron motion will be addressed. Two strategies—already realized experimentally—are presented: control of electron dynamics via the carrier envelope phase (CEP) in few-cycle pulses and via the temporal phase of a femtosecond laser pulse with attosecond precision. The issue of nuclear and electronic wavepacket synchronization to achieve control on a chemical reaction is raised. A theoretical method to answer these questions is presented. Finally, a proposal how the electron dynamics can be used as an additional control parameter for a chemical reaction is made.
Sebastian Thallmair, Robert Siemering, Patrick Kölle, Matthias Kling, Matthias Wollenhaupt, Thomas Baumert, Regina de Vivie-Riedle
9. The Dynamics of Quantum Computing in Molecules
Abstract
A brief introduction to quantum computing is provided and the potential use of molecules as the platform is discussed. The basic building blocks (quantum bits, quantum gates, and quantum algorithms) are described in order to emphasize the requirements for realizing a quantum computer, and, the advantages quantum computation has over its classical counterpart. We outline the three key steps to quantum computation: (1) initialization, (2) manipulation, and (3) readout. The possible use of internal molecular states as quantum bits and shaped laser fields to implement the quantum gates is introduced. The application to molecular quantum computing is connected to the more general problem of the control of quantum dynamics using tailored laser fields determined theoretically with optimal control theory or genetic algorithms.
Alex Brown, Ryan R. Zaari
10. Conclusions
Abstract
The first stage in the history of molecular quantum dynamics has been dedicated mainly to the development of numerical methods for solving the Schrödinger equation. Nowadays, the main challenge is to reproduce experimental data at a very high level of accuracy for small molecular systems in the gas phase. Many examples have been given in the present book. The systems contain up to 4–10 atoms in full dimensionality depending on their complexity.
Fabien Gatti, Benjamin Lasorne
Metadaten
Titel
Molecular Quantum Dynamics
herausgegeben von
Fabien Gatti
Copyright-Jahr
2014
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-642-45290-1
Print ISBN
978-3-642-45289-5
DOI
https://doi.org/10.1007/978-3-642-45290-1

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