CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

insight about the electronic structure of the cluster. 27-29 .In this context, many anionic
systems are studied experimentally to understand microsolvation but very less theoretical
attempts are available. 9,22,30-32 All the theoretical analysis on IR and PES spectra is based
on a few most stable structures of the finite size clusters. But, with the increase in number
of solvent water molecules in solvated clusters, the number of minimum energy
configurations with close in energy for each size of clusters is expected to increase.
Experimental observation on a particular size of cluster includes contribution from all
possible minimum energy structures, which survive at that particular conditions of the
experiment. Only average information is obtained from the experimental method. To
predict a theoretical energetics and spectral properties of a microhydrated system, one has
to take into account the contribution of all possible minimum energy structures for a
particular size of the cluster, resulting in a weighted average energetics and spectral
properties. However no such attempt has been reported in the literature. A part of the
thesis is devoted to predict energetics and spectral properties based on a weighted
average procedure. The weight factor is calculated following the free energy based
Boltzmann population analysis at a finite temperature.
1.2.4. Connecting Cluster Properties to that of the Bulk
Molecular cluster acts as an intermediate state between isolated gaseous molecule
and condense phase bulk system. Several efforts are being made to connect molecular
cluster properties of a chemical species to its bulk properties. It is well known that in
solution (bulk) many important properties of a chemical species are often widely different
from those in the isolated gas phase. The structure and energetics of the cluster of a
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