Energetics and transition-state dynamics of the F + HOCH₃ → HF + OCH₃ reaction

The F + HOCH₃ → HF + OCH₃ reaction is a system with 15 internal degrees of freedom that can provide a benchmark for the development of theory for increasingly complex chemical reactions. The dynamics of this reaction were studied by photoelectron-photofragment coincidence (PPC) spectroscopy carried out on the F^-(HOCH₃) anion, aided by a computational study of both the anion and neutral potential energy surfaces, with energies extrapolated to the CCSDT(Q)/CBS level of theory. Photodetachment at 4.80 eV accesses both the reactant and product channels for this reaction. In the product channel (HF + OCH₃ + e^-) of the neutral potential energy surface, vibrationally excited HF products in addition to the stable product-channel hydrogen-bonded complex (FH-OCH₃) are observed in the PPC and photoelectron spectra. In addition, experimental evidence is observed for the reactant-channel van der Waals complex (F-HOCH₃), in good agreement with the theoretical predictions. The relative stability of these long-lived complexes was probed by reducing the ion beam energy, increasing the product time-of-flight, indicating lifetimes on the microsecond timescale for the reactant- and product-channel complexes as well as providing evidence for long-lived vibrational Feshbach resonances associated with the HF(v > 0) + OCH₃ product states. This system will provide a model for extending full-dimensionality quantum dynamics to larger numbers of degrees of freedom.