CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

ammonia. 61-62 Hydrogen bonded water clusters with alkali metal atom residing in the
cluster cavity (M.nH 2 O) have also been studied to a great extent. 63-67,17
Solvated electrons can form rather readily with the alkali metals in polar solvent
because of the relatively low energy requirement for ionization. The most familiar case
occurs in the solvent stabilization of alkali metal atoms in bulk ammonia, where optical
transitions involving these electrons are responsible for the strong colors of the resulting
solutions. The formation of solvated electron in finite size clusters is also expected. A
number of theoretical and experimental efforts have been put to gather knowledge on
ammonia clusters in presence of Li, Na and Cs alkali metal atoms in the context of
solvated electron. 16-17,66-72 In this chapter, structure, energy parameters and IR spectra of
ammonia clusters in presence of a potassium metal atom (K.nNH 3 , n=1-6) based on first
principle electronic structure theory is presented to study the process of microsolvation in
ammonia medium. Studies on these size selected clusters play a critical role to follow the
evolution of molecular level properties with the size of the cluster in gas phase and to
bridge the gap between the properties of single ammonia cluster (K-NH 3 ) to the bulk
solution of K metal in ammonia solvent. The variation of calculated properties with size
(n) of the clusters, K.nNH 3 is also reported. As a number of minimum energy structures
are predicted for higher cluster, weighted average properties of the clusters are calculated
based on the statistical population of different minimum energy structures at 150 K.
6.2. Theoretical Approach
Full geometry optimization of ammoniated clusters has been carried out without
any symmetry restriction to locate minimum energy structures applying a nonlocal hybrid
95