Probing the Transition State with Negative Ion Photodetachment: The Cl +HCl and Br + HBr Reactions.

摘要

The transition-state region for neutral hydrogen-transfer reactions can be probed by photodetaching the appropriate stable, hydrogen-bonded negative ion. This paper presents a detailed account of this method, in which the Cl + HCl and Br + HBr reactions are investigated by photoelectron spectroscopy of ClHCl-, BrHBr-, and the corresponding deuterated species. The photoelectron spectra exhibit resolved vibrational structure attributed to the unstable neutral (ClHCl) or (BrHBr) complex. The peaks in the spectra are assigned to the antisymmetric stretch mode of the complex, and the peak widths are sensitive to the lifetime of the complex. The BrHBr- and BrDBr- spectra exhibit narrow (15-20 meV) peaks that are likely to result from reactive resonance states supported by the Br + HBr potential energy surface, as well as peaks that appear to be from an electronically excited state of the (BrHBr) complex. The BrHBr- and BrDBr- results have been analyzed to yield an 'effective' collinear potential energy surface for the Br + HBr reaction. Reprints. (jes)