CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

due to Mayer. 58 The calculated bond distance (r xx ) and bond order (B xx ) between two
halogen atoms do not show any significant variation on addition of successive solvent
water molecules. From the structural information it is noted that only a few water
molecules are in close surrounding of halogen (X 2 ) moiety.
4.3.3. Solvent Stabilization and Interaction Energy
Solvent stabilization energy of these clusters X 2 .nH 2 O (X=Cl, Br & I) may be
expressed as
E solv = E X2. nH2O – (nE H2O + E X2 )
where E X2. nH2O refers to the energy of the cluster X 2 .nH 2 O (X=Cl Br and I). E H2O and E X2
refer to the energy of a single H 2 O and X 2 (X=Cl, Br & I) system. Thus, the calculated
solvent stabilization energy represents the solvent stabilization of the molecular cluster
on addition of successive solvent water molecules accounting interaction of halogen
atoms with water units as well as inter water H-bonding. The solvent stabilization energy
of the X 2 .nH 2 O (X=Cl, Br & I) clusters calculated at MP2/6-311++G(d,p) level of theory
(for I 6-311 basis is used) are provided in Table 4.1. The variation of solvation energy
(E solv ) vs. n, number of water molecules in X 2 .nH 2 O cluster (X=Cl, Br & I) are displayed
in Fig.4.2 (A-C), respectively, showing a continuous increase on addition of each solvent
water unit. As expected, the calculated solvent stabilization energy is very small
compared to the same calculated for charged systems, X •− 2 .nH 2 O (as discussed in Chapter
2).
It is clearly seen from Table 4.1 that the solvent stabilization energy is the highest
for I 2 .nH 2 O system. But between Cl 2 .nH 2 O and Br 2 .nH 2 O systems the solvent
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