Nonadiabatic transitions, spin-orbit coupling, and prereactive complexes in polyatomic reaction dynamics
Final Report Abstract
The project focused on the fundamental understanding of elementary chemical reaction processes in polyatomic systems and investigated the effect of non-adiabatic transitions, spin-orbit coupling, and prereactive complex formation. Reactions of fluorine and chlorine with methane were considered as prototypical examples which are intensively studied by experiment and theory. Atoms as fluorine or chlorine show degenerate electronic states which give rise to vibronic and spin-orbit coupling effects in the entrance channel of the reaction. The reactions have previously been studied only on a single adiabatic potential energy surface and the effect of non-adiabatic transitions had been ignored. Coupled diabatic potential energy surface are a prerequisite for accurate quantum dynamics calculations but their construction is a challenging issue. In the present project, a systematic approach to construct accurate global diabatic potential energy surfaces including vibronic and spin-orbit couplings for X(P)+CH4 →HX+CH3 reactions has been introduced. It has been successfully applied to obtain full-dimensional (12D) coupled diabatic potentials describing the F(2 P)+CH4 →HF+CH3 and Cl(2 P)+CH4 →HCl+CH3 reactions for the first time. These potentials provide the basis for accurate quantum dynamics simulations of these reactions including the non-adiabatic effects. Reduced-dimensional (8D) wave packet calculations studying the F(2 P)+CH4 →HF+CH3 reaction found prominent resonance structures resulting from the formation of a long-living prereactive F·CH4 complex in the entrance channel of the reaction. Results of trajectory surface hopping calculations indicate that non-adiabatic transitions increase the reaction probability for F-atoms in the 2 P3/2 as well as in the 2 P1/2 electronic state. Full-dimensional (12D) quantum dynamics calculations investigated the quasi-bound states of the F·CH4 complex in detail. For a model which ignores the breakdown of the Born-Oppenheimer approximation due to vibronic coupling, the resulting energy levels could be assigned and an inituitive understanding of underlying quantum dynamics could be achieved. The situation changed dramatically if vibronic and electonic angular momentum couplings were correctly considered. The resulting eigenstates could no longer be assigned and an apparently chaotic energy level structure was found. Thus, for the individual resonances a profound effect resulting from the non-adiabatic coupling was found. In contrast, statistical properties were only moderately affected by the non-adiabatic coupling.
Publications
- Communication: Mode specific quantum dynamics of the F+CHD3 →HF+CD3 reaction, J. Chem. Phys. 144, 171101 (2016)
Ji Qi, Hongwei Song, Minghui Yang, Juliana Palma, Uwe Manthe, and Hua Guo
(See online at https://doi.org/10.1063/1.4948547) - Quasi-Bound States of the F·CH4 Complex, J. Phys. Chem. A 120, 3186 (2016)
Daniela Schäers and Uwe Manthe
(See online at https://doi.org/10.1021/acs.jpca.5b11694) - Neural network based coupled diabatic potential energy surfaces for reactive scattering, J. Chem. Phys. 147, 084105 (2017)
T. Lenzen and Uwe Manthe
(See online at https://doi.org/10.1063/1.4997995) - Non-adiabatic effects in F + CHD3 reactive scattering, J. Chem. Phys. 146, 214117 (2017)
J. Palma and Uwe Manthe
(See online at https://doi.org/10.1063/1.4984593) - Coordinate systems and kinetic energy operators for multi-configurational time-dependent Hartree calculations studying reactions of methane, Chem. Phys. 509, 37 (2018)
Daniela Schäers, Bin Zhao, and Uwe Manthe
(See online at https://doi.org/10.1016/j.chemphys.2018.02.025) - Vibronically and spin-orbit coupled diabatic potentials for X(P)+CH4 → HX + CH3 reactions: General theory and application for X(P)=F(2 P), J. Chem. Phys. 150, 064102 (2019)
Tim Lenzen and Uwe Manthe
(See online at https://doi.org/10.1063/1.5063907)
