PROBING THE TRANSITION-STATE WITH NEGATIVE-ION PHOTODETACHMENT - THE CL + HCL AND BR + HBR REACTIONS

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. © 1990 American Chemical Society.