Mode-selective chemistry and quantum state resolved polyatomic reaction dynamics
Final Report Abstract
The project investigated the dynamics of polyatomic reactions on a detailed quantum stateresolved level. Reactions of methane with atoms and diatoms were studied. These reactions are important processes in atmospheric and combustion chemistry as well as prototypical examples of polyatomic reaction processes intensively studied in fundamentally oriented research. Accurate first principles-based quantum theory was successfully employed to investigate the reaction dynamics in detail. Correlations between the quantum states of the reactants and products in a six atom reaction were studied for the first time by rigorous full-dimensional quantum dynamics calculations. The calculations demonstrated the crucial importance of the transition state for the modespecific chemistry observed in these reactions. The quantum state distribution of the reaction products is determined by the geometry of the effective transition state. For the H+CH4 → H2 +CH3 reaction, a loss of vibrational memory was observed: here the quantum state distribution of the products is essentially independent of the vibrational excitation of the reactants and results from a sudden decay of the activated complex. More subtle variations of the underlying principle could be identified studying the H+CHD3 → H2 +CD3 reaction: vibrational excitation of the reactant can slightly alter the geometry of the effective dynamical transition state and thereby indirectly affect the product distribution. The resulting picture of quantum state-specific chemistry can be viewed as a natural extension of standard textbook chemistry: the transition state plays the key role and control of the reaction path can be achieved via designed modifications of the transition state. The dependence of a molecule’s reactivity on its initial vibrational quantum state can be explained along the same lines if the principle of microscopic reversibility is utilized and the sudden decay of the activated complex towards reactant is considered. The quantum states of the reactants which are most strongly populated in course of this decay are the ones which show the highest reactivity. While most results can be explained using these simple and intuitive ideas, further complexity can appear as a consequence of system-specific quantum effects, e.g., the reactivity borrowing resulting from Fermi resonance-type state mixing.
Publications
- Full-dimensional and reduced-dimensional calculations of initial state-selected reaction probabilities studying the H+CH4 → H2 +CH3 reaction on a neural network PES, J. Chem. Phys. 142, 064309 (2015)
R. Welsch and U. Manthe
(See online at https://doi.org/10.1063/1.4906825) - Loss of Memory in H+CH4 → H2 +CH3 State-to-State Reactive Scattering, J. Phys. Chem. Lett. 6, 338 (2015)
R. Welsch and U. Manthe
(See online at https://doi.org/10.1021/jz502525p) - S-matrix decomposition, natural reaction channels, and the quantum transition state approach to reactive scattering, J. Chem. Phys. 144, 204119 (2016)
U. Manthe and R. Ellerbrock
(See online at https://doi.org/10.1063/1.4952478) - A transition-state based rotational sudden (TSRS) approximation for polyatomic reactive scattering, J. Chem. Phys. 147, 144104 (2017)
B. Zhao and U. Manthe
(See online at https://doi.org/10.1063/1.5003226) - H+CH4 → H2 +CH3 initial state-selected reaction probabilities on different potential energy surfaces, Chem. Phys. 482, 106 (2017)
R. Ellerbrock and U. Manthe
(See online at https://doi.org/10.1016/j.chemphys.2016.08.032) - Communication: Reactivity borrowing in the mode selective chemistry of H+CHD3 → H2 +CD3 , J. Chem. Phys. 147, 241104 (2018)
R. Ellerbrock and U. Manthe
(See online at https://doi.org/10.1063/1.5018254) - Full-dimensional quantum dynamics calculations for H+CHD3 → H2 + CD3 : The effect of multiple vibrational excitations, J. Chem. Phys. 148, 224303 (2018)
R. Ellerbrock and U. Manthe
(See online at https://doi.org/10.1063/1.5037797) - Natural reaction channels in H+CHD3 → H2 + CD3, Faraday Disc. 212, 217 (2018)
R. Ellerbrock and U. Manthe
(See online at https://doi.org/10.1039/c8fd00081f) - Counter-propagating wave packets in the quantum transition state approach to reactive scattering, J. Chem. Phys. 150, 184103 (2019)
B. Zhao and U. Manthe
(See online at https://doi.org/10.1063/1.5097997) - Direct product-type grid representations for angular coordinates in extended space and their application in the MCTDH approach, J. Chem. Phys. 154, 104115 (2021)
B. Zhao and U. Manthe
(See online at https://doi.org/10.1063/5.0045054)
