Vibronic coupling in the F·CH4 prereactive complex.

The F + CH4 → HF + CH3 reaction shows a counter-intuitive mode-selective chemistry and prominent resonances. The prereactive F·CH4 complex formed in the entrance channel is assumed to play an important role in the dynamics of the reaction. The present work investigates the effect of nonadiabatic transitions and the geometric phase on the low-lying quasibound states of the F·CH4 complex. Quantum dynamics calculations employing the multiconfigurational time-dependent Hartree approach and accurately accounting for vibronic as well as spin-orbit coupling are performed. Extending previous work [D. Schäpers and U. Manthe, J. Phys. Chem. A 120, 3186 (2016)], which was restricted to the dynamics on a single adiabatic potential energy surface and found the relative rotation of F and CH4 to proceed almost freely, we found chaotic patterns if vibronic coupling is included. While nonadiabatic transitions strongly affect individual resonances, their effect on averaged quantum state densities and the photodetachment spectrum of F⋅CH4 - is found to be minor.