Negative-ion photodetachment as a probe of bimolecular transition states: the F + H2 reaction

The transition-state region of the F + H2, F + D2 and F + HD reactions has been studied by photoelectron spectroscopy of the negative ions FH–2, FD–2 and FDH–. Photodetachment of these anions can access three electronic states of the neutral, but transitions to the ground-state potential-energy surface for the reaction can be observed selectively by adjusting the polarization of the photodetachment laser. Under these conditions, the FH–2 spectrum is similar to the recent simulation by Zhang and Miller which used the T5a potential-energy surface for the F + H2 reaction. The spectra of all three isotopic anions are interpreted by comparison to previous reactive scattering calculations. This comparison strongly suggests that several of the peaks in the photoelectron spectra are due to transitions to scattering resonances.