The reaction F + H2O → 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-(H2O) 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 hνUV = 4.80 eV, the overtone of the ionic hydrogen bond mode in the precursor F-(H2O), 2νIHB 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 + H2O 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.

Background: Optical access to a travelling ion packet is required in many ion beamexperiments that study ion-photon interactions.Methods: An approach is described for carrying out direct infrared excitation of a fastion beam that uses an optical-quality reflective beam blocker to illuminate a counterpropagating pulsed ion beam in a collinear configuration. This arrangement providesoptical access along the axis of ion beam propagation by placing a mirror in the beampath at a 25 degree angle. The ion packet is bumped over the mirror, which is alsoused to block fast neutral particles produced during ion beam acceleration that alsopropagate along the beam path.Results: The efficiency of this setup is demonstrated in a photodetachment experimenton NO− anions, where a photoinduced depletion of up to 90% of the beam is achievedin a single laser shot. To demonstrate the application of this configuration, the relativephotodetachment cross section for NO− has been measured in the range of 2800 –7200 cm-1. The measured relative cross section shows a set of sharp peaks that areidentified as vibrational autodetachment resonances.Conclusion: The new setup paves the way for future experiments where parentanionic species are vibrationally excited via direct infrared excitation first andundergo photodetachment/photodissociation in a subsequent step.