Effects of vibrational excitation on the F + H 2 O → HF + OH reaction: dissociative photodetachment of overtone-excited [F-H-OH] .

The reaction F + H2 O → HF + OH is a four-atom system that provides an important benchmark for reaction dynamics. Hydrogen atom transfer at the transition state for this reaction is expected to exhibit a strong dependence on reactant vibrational excitation. In the present study, the vibrational effects are examined by photodetachment of vibrationally excited F- (H2 O) precursor anions using photoelectron-photofragment coincidence (PPC) spectroscopy and compared with full six-dimensional quantum dynamical calculations on ab initio potential energy surfaces. Prior to photodetachment at hν UV = 4.80 eV, the overtone of the ionic hydrogen bond mode in the precursor F- (H2 O), 2 ν IHB at 2885 cm-1 , was excited using a tunable IR laser. Experiment and theory show that vibrational energy in the anion can be effectively carried away by the photoelectron upon a Franck-Condon photodetachment, and also show evidence for an increase of branching into the F + H2 O reactant channel. The experimental results suggest a greater role for product rotational excitation than theory. Improved potential energy surfaces and longer wavepacket propagation times would be helpful to further examine the nature of the discrepancy.