Quasi-Bound States of the F·CH4 Complex

The F + CH4 → HF + CH3 reaction is an intensively studied prototypical example of a polyatomic reaction showing an early transition state. Prereactive complexes are assumed to play an important role in the dynamics of the reaction. In this work, the long-living resonance states resulting from the formation of a metastable F·CH4 complex are investigated in detail. Full-dimensional quantum dynamics calculations employing the multiconfigurational time-dependent Hartree (MCTDH) approach and a single adiabatic potential energy surface are used to study the low-lying quasi-bound states of the F·CH4 complex for vanishing total (nuclear) angular momentum. The computed dissociation energy of the F·CH4 complex with respect to the reactant asymptote is 170 cm(-1). About 60 resonance states with energies below the reactant asymptote are found. A detailed analysis of the computed wave function of the low-lying states shows an almost free relative rotation of F and CH4 and an approximately separable F-CH4 stretching vibration. The present results are compared with transition state spectroscopy experiments which study the photodetachment spectrum of the CH4F(-) anion.