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Chemical Reaction Dynamics and Potential Ridge: Beyond the Transition State
Published in Takayuki Fueno, The Transition State, 2019
The chapter is organized as follows. In Section 10.2 the hyperspherical coordinate approach and the corresponding scattering equations are summarized and the basic physical quantities defined. Section 10.3 emphasizes the role of potential ridge, and presents some examples to demonstrate its significance for a qualitative understanding of reaction dynamics under the regime of the reduced dimensionality approximations.2,5)Section 10.4 discusses the quantum mechanically accurate treatments of triatomic systems. By taking reaction systems such as D + H2, Cl + H2, O + HCl and Mu + H2 studied by the author’s group,6–10) various aspects of the reaction dynamics such as effects of potential energy surface topography, isotope effect, effects of initial internal states and final internal state distribution are discussed. Section 10.5 provides concluding remarks, and also summarizes problems for further investigation and future perspectives from the author’s point of view.
Picometer Detection by Adaptive Holographic Interferometry
Published in Klaus D. Sattler, Fundamentals of PICOSCIENCE, 2013
HHG has many future applications. It is a laboratory-scale source of XUV and soft x-ray photons with femtosecond and attosecond durations that can be used to form microscopic images of materials or to time-resolve the motion of electrons within atoms and molecules. HHS can be applied to understanding the electronic structure of atoms and molecules. In the case of molecular dynamics, knowledge of the amplitude and phase of the photorecombination moment relative to a fully characterized ground state reference [32] will allow the dynamic imaging of orbitals in a chemical reaction. The unique properties of HHS will lead to other applications in femtochemistry, from simple dissociation dynamics, to proton transfer, to non-adiabatic reaction dynamics, to complex photochemical processes. For example, the change in electronic structure associated with the crossing of a conical intersection [101-103] will be mapped into the harmonic radiation. In all these cases, the sensitivity of HHS to the electronic structure will provide new insight.
Molecular Beam Scattering: Reactive Scattering
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
There remain a wide range of heterogeneous reaction systems that have not been fully explored in terms of mechanism, kinetics, or dynamics. The tool of reactive molecular beam scattering from surfaces promises to be an effective one in carrying out this exploration. This approach is unsurpassed in providing detailed kinetic and dynamic information about reactions on well-characterized solid surfaces. While spectroscopic probing of adsorption and reaction will certainly continue to provide the bulk of our information about the chemistry of surfaces, the unique information that is available from the heterogeneous processes. This sort of information will begin to put the understanding of surface chemistry on the same footing as our detailed knowledge of elementary reactions in the gas phase. State-specific reaction scattering approach described here will set the standard for the understanding of elementary reaction dynamics, an understanding of the effect of surface structure and composition on reaction mechanism, the construction of the potential energy surface governing surface reactions, and general rules for the prediction of heterogeneous reactivity and selectivity are the fruits we can expect from the application of this powerful approach to the study of surface chemistry.
Vibrational, non-adiabatic and isotopic effects in the dynamics of the H2 + H2 + → H3 + + H reaction: application to plasma modelling
Published in Molecular Physics, 2023
P. del Mazo-Sevillano, D. Félix-González, A. Aguado, C. Sanz-Sanz, D.-H. Kwon, O. Roncero
This work is organised as follows. In Section 2, we develop new potential energy surfaces (PESs), which include non-adiabatic effects and increase the accuracy of the fit. This new fit uses a Neural Network (NN) method to describe the four-body term, to improve a zero-order description using a Triatomics-in-Molecule treatment, which accurately fits very precise ab initio calculations, over a broader energy interval than previous fits, up to 17 eV. In Section 3, we study the reaction dynamics using a quasi-classical trajectory (QCT) method, including transitions among different electronic states, using the fewest switches method of Tully [66]. The reaction dynamics is studied for collision energies between 1 meV and 10 eV, and for several vibrational states of reactant, as well as for the deuterated reaction, focussing on high energy reactive cross sections recently measured by Savic et al. [65]. In Section 4, we investigate how the calculated reactive cross sections affect the population density of and D in CR models of /D plasma. Finally, in Section 5 some conclusions are extracted.
A Reactive Molecular Dynamics Investigation of Nanoparticle Interactions in Hydrocarbon Combustion
Published in Combustion Science and Technology, 2023
Majd Sayed Ahmad, Efstratios M. Kritikos, Andrea Giusti
To give more insight into the transient combustion mechanism of a nanoparticle in a gas mixture of n-C7H16 and oxygen, simulations with the NVE canonical ensemble are discussed below. This section relies on results obtained with the QEq charge equilibration method only, since it offers overall accelerated kinetics (as shown in Figure 3), thus reducing the necessary computational time. The time evolution of the system’s temperature is shown in Figure 5. The overall behavior of the system did not show significant variations for different initial temperature conditions of the gas mixture and nanoparticle. This suggests that the trajectory of the system is mainly dependent on the particle energy content and its release during the reaction dynamics. As observed in Figure 5, the combustion process of AlNP systems can be divided into three stages. The first stage is characterized by a rapid heating. Subsequently, the heating rate decreases (second stage), followed by the convergence of the system’s temperature. During the first stage (i.e., below 0.2 ns of simulated time), AlNP combustion showcased a relatively high heating rate (). The heating rate appears to be in agreement with NVE simulations conducted by Liu, Wang, and Liu (2018) for AlNP oxidation. This suggests that a very rapid particle ignition takes place. Following the ignition process, a large amount of heat is released, accounting for 80% of the temperature buildup (Figure 5). The second stage (time period between 0.2 ns and 0.55 ns) is characterized by an approximately linear increase of the system’s temperature. In the third stage, the system reaches a steady-state combustion process at constant temperature K.
Dynamical investigations of the O(3P) + H2O reaction at high collision energies on an accurate full-dimensional potential energy surface
Published in Molecular Physics, 2021
Based on the LDG PES [39], the VENUS chemical reaction dynamics programme [44] is used for the full-dimensional quasi-classical trajectory (QCT) calculations of the reactions between O(3P) and H2O. As shown in Figure 1, the following events are needed to be considered,