CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

CHAPTER 5
UV-Vis Spectra of Anionic Hydrated Clusters: Extrapolation
to Bulk
5.1. Introduction
Recently, a few attempts are being made to reproduce the bulk properties, like
detachment energies of the excess electron of bulk solute solution (aqueous) from the
knowledge of finite size anionic hydrated cluster data applying size selected
photoelectron spectroscopy. 9,33-35 UV-Vis spectra of many transients in aqueous solution
(bulk) are widely applied to study complex chemical reaction. However, no effort is
made to connect UV-Vis spectra of a solute in aqueous solution to that of its finite size
hydrated clusters. In this regard, hydrated clusters of Cl • 2 ⎯, Br • 2 ⎯, I • 2 ⎯ and CO • 3 ⎯ are
studied following first principle based theoretical methods to understand the origin of
UV-Vis transition and to extract bulk optical absorption spectra of these radical anions in
their respective aqueous solution. This study is very useful to those who practice
radiation chemistry. In aqueous solution, hydroxyl radical ( • OH) reacts with X¯ (X=Cl,
Br &I) to form a transient species, which has a broad and strong absorption in the UVvisible
region. 3,59 This absorption maximum is assigned to the halogen dimer radical
anion species, X 2•¯( X=Cl, Br &I), a specific one electron oxidising species. It is reported
that Cl 2•¯, Br 2•¯ and I 2•¯ species absorb strongly in their respective aqueous solution with
absorption maximum (λ max ) at 340, 360 and 380 nm, respectively. Similarly, hydroxyl
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