Experimental and theoretical study of the O+HCl transition state region by photodetachment of OHCl^-

We present measured and calculated photodetachment spectra of OHCl ^-, and we interpret the results in terms of the vibrational structure of the transition state of the O+HCl→OH+Cl reaction. The measured spectra exhibit two distinct features - an intense broad peak at high electron kinetic energies and a less intense shoulder at lower energies. Superimposed on these broad features are several sharper structures, but they are barely discernible from noise in the spectrum. To interpret these spectra, we have used a recently developed global ³A″ potential surface for the O+HCl reaction to calculate Franck-Condon factors, using an L² method (i.e., expansion in terms of square integrable basis functions) to approximate the scattering wave functions on the reactive surface. Assignment of the spectrum has been assisted using the results of quantum coupled channel calculations for the same surface. The resulting calculated spectrum shows the same broad features as the measured spectrum. There is also fine structure with spacings and energies that are similar to the experiment, but specific features do not match. To interpret both the broad and fine features in the theoretical spectrum, a hierarchical analysis is applied wherein this spectrum is decomposed by a tree construction into components of increasingly higher resolution. The physical meaning of each of these components is then determined by plotting "smoothed states" that are obtained from the tree coefficients. This leads to the conclusion that the two broad features in the spectrum are made up of progressions in hindered rotor states of the Cl-OH complex, with the most intense feature corresponding to OH(v=0) and the weaker shoulder corresponding to OH(v=1). There is evidence for Feshbach resonance features in the v=1 feature, but it appears that most of the fine structure is due to hindered rotor states.