Initial state‐selected reaction probabilities for OH+H2→H+H2O and photodetachment intensities for HOH− 2

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/101/10/10.1063/1.468057.We have used a discrete variable representation (DVR) with absorbing boundary conditions (ABC) to calculate initial state‐selected reaction probabilities and photodetachment intensities. We apply this method to the OH+H2reaction constrained to a plane with the OH bond frozen. The calculated reaction probabilities have all the qualitative features observed in full dimensional calculations. We have similarly computed arrangement‐selected photodetachment intensities for one geometry of the HOH− 2 anion. The resulting spectrum has a dominant peak which will present a test of the neutral potential energy surface upon comparison with experimental results

Wave packet dynamics in the optimal superadiabatic approximation

We explain the concept of superadiabatic approximations and show how in the context of the Born- Oppenheimer approximation they lead to an explicit formula that can be used to predict transitions at avoided crossings. Based on this formula, we present a simple method for computing wave packet dynamics across avoided crossings. Only knowledge of the adiabatic electronic energy levels near the avoided crossing is required for the computation. In particular, this means that no diabatization procedure is necessary, the adiabatic energy levels can be computed on the fly, and they only need to be computed to higher accuracy when an avoided crossing is detected. We test the quality of our method on the paradigmatic example of photo-dissociation of NaI, finding very good agreement with results of exact wave packet calculations.Comment: 12 pages, 6 figure

An efficient scheme for numerical simulations of the spin-bath decoherence

We demonstrate that the Chebyshev expansion method is a very efficient numerical tool for studying spin-bath decoherence of quantum systems. We consider two typical problems arising in studying decoherence of quantum systems consisting of few coupled spins: (i) determining the pointer states of the system, and (ii) determining the temporal decay of quantum oscillations. As our results demonstrate, for determining the pointer states, the Chebyshev-based scheme is at least a factor of 8 faster than existing algorithms based on the Suzuki-Trotter decomposition. For the problems of second type, the Chebyshev-based approach has been 3--4 times faster than the Suzuki-Trotter-based schemes. This conclusion holds qualitatively for a wide spectrum of systems, with different spin baths and different Hamiltonians.Comment: 8 pages (RevTeX), 3 EPS figure

Bond breaking in vibrationally excited methane on transition metal catalysts

The role of vibrational excitation of a single mode in the scattering of methane is studied by wave packet simulations of oriented CH4 and CD4 molecules from a flat surface. All nine internal vibrations are included. In the translational energy range from 32 up to 128 kJ/mol we find that initial vibrational excitations enhance the transfer of translational energy towards vibrational energy and increase the accessibility of the entrance channel for dissociation. Our simulations predict that initial vibrational excitations of the asymmetrical stretch (nu_3) and especially the symmetrical stretch (nu_1) modes will give the highest enhancement of the dissociation probability of methane.Comment: 4 pages REVTeX, 2 figures (eps), to be published in Phys. Rev. B. (See also arXiv:physics.chem-ph/0003031). Journal version at http://publish.aps.org/abstract/PRB/v61/p1565

Homeomorphisms generated from overlapping affine iterated function systems

We develop the theory of fractal homeomorphisms generated from pairs of overlapping affine iterated function systems

Roadmap on dynamics of molecules and clusters in the gas phase

This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science

Calculating vibrational spectra using modified Shepard interpolated potential energy surfaces

A potential energy interpolation approach based on modified Shepard interpolation and specifically designed for calculation of vibrational states is presented. The importance of the choice of coordinates for the rate of convergence is demonstrated. Studying the vibrational states of the water molecule as a test case, a coordinate system comprised of inverse bond distances and trigonometric functions of the bond angle is found to be particularly efficient. Different sampling schemes used to locate the reference points in the modified Shepard interpolation are investigated. A final scheme is recommended, which allows the construction of potential energy surfaces to sub-wave-number accuracy. © 2008 American Institute of Physics

Accurate calculations of reaction rates: predictive theory based on a rigorous quantum transition state concept

Manthe U. Accurate calculations of reaction rates: predictive theory based on a rigorous quantum transition state concept. Molecular Physics. 2011;109(11):1415-1426.In recent years the accurate and truly predictive calculation of thermal rate constants has become feasible for reactive systems consisting of more than only three or four atoms and results for benchmark six atom reactions as H + CH4 -> H-2 + CH3 were presented. The present article reviews research focusing on the accurate calculation of rates for reactions proceeding via barriers and highlights key method developments as well as important applications in the area. It discusses the quantum transition state concept which allows one to rigorously and efficiently compute averages with respect to thermal or micro-canonical ensembles and to interpret the results using intuitive pictures. Schemes for the construction of accurate high-dimensional potential energy surfaces required in quantum dynamics simulations and for performing efficient multi-dimensional wave packet dynamics calculations are also reviewed. As a result of the large number of accurate reaction rate calculations for diverse reactions which have been presented in about the last decade, a consistent picture of the importance of quantum effects in reaction rates emerged. The present article attempts to comprehensively describe this picture and in addition will try to provide guidelines when significant deviations for classical (harmonic) transition state theory can be excepted

Loss of Memory in H + CH4 -> H-2 + CH3 State-to-State Reactive Scattering

Welsch R, Manthe U. Loss of Memory in H + CH4 -> H-2 + CH3 State-to-State Reactive Scattering. The Journal of Physical Chemistry Letters. 2015;6(3):338-342.State-to-state reaction probabilities for the H + CH4 -> H-2 + CH3 reaction are calculated by accurate full-dimensional quantum dynamics calculations employing the multilayer multiconfigurational time-dependent Hartree approach and the quantum transition-state concept. Reactions starting from different vibrational and rotational states of the methane reactant are investigated for vanishing total angular momentum. The vibrational state distributions of the products are found to be essentially independent of the initial rovibrational state of the reactants. The reaction products only show vibrational excitation in the methyl umbrella mode. No excitation in H-2 vibration or another CH3 vibration is observed. Analyzing the results, the observed loss of vibrational memory can be explained by a transition-state-based view of the reaction process