Transition state spectroscopy of the I + HI reaction in clusters: Photoelectron spectroscopy of IHI− ·Arn (n = 1–15)

Abstract

We have investigated effects of solvation on the transition state spectroscopy and dynamics of the I + HI reaction by measuring the anion photoelectron (PE) spectra of the clusters IHI⁻·Ar_n (n = 1–5). Argon clustering results in a successive shift of the PE spectra to lower electron kinetic energies with increasing cluster size. It also leads to significant vibrational cooling in the PE spectra and facilitates the observation of features associated with symmetric stretch vibrations and hindered rotational motions of the transition state complex IHI. The shifts in electron binding energy suggest that the first six argon atoms form a ring around the waist of the IHI⁻ anion, just as in I₂⁻·Ar_n. The spacing of the antisymmetric stretch features evolves with cluster size and is attributed at least in part to perturbation of the IHI⁻ geometry in larger argon clusters. Intensities of features due to hindered rotation are enhanced for larger clusters, possibly due to solvent perturbation of the neutral transition state region.