CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

and Raman spectroscopic studies is also interesting to study the microsolvation of I •− 2 in
CO 2 . In what follows, a systematic theoretical study on structure, energetics (solvent
stabilization, interaction and vertical detachment energy) and spectra (both IR and
Raman) of I •− 2 .nCO 2 clusters (n=1-10) is presented to elucidate the effect of
microsolvation in this chapter.
7.2. Theoretical Approach
It is reported in the literature that BHHLYP functional performs well to describe
such open shell doublet systems. 43-44 Energy parameters are further improved by single
point energy calculations applying second order Moller-Plesset (MP2) perturbation
theory adopting 6-311+G(d) basis sets. Quasi Newton Raphson based algorithm as well
as Monte Carlo based simulated annealing procedures have been applied with the
effective fragment solvent CO 2 molecules to find out the global minimum energy
structure of different size molecular clusters. 36 Hessian calculations have been performed
for all the optimized minimum energy structures to check the nature of the equilibrium
geometry and to generate IR spectrum. Raman spectrum is also calculated for all the
clusters. Basis sets 6-311G(d) for I is obtained from the Extensible Computational
Chemistry Environment Basis Set Database, Pacific Northwest National Laboratory.
7.3. Results and Discussions
7.3.1. Structure
It is observed that, in this system the conformers of a particular size of cluster is
very close in energy (within 0.3 kcal/mol) and have near equal statistical contribution.
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