CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

311++G(d,p) level of theory. The λ max values of the Cl •− 2 .nH 2 O clusters (n=1-11)
calculated at same level of theory are listed in Table 5.1.
Excited state calculations at CIS/6-311++G(d,p) level of theory suggest that
Cl •− 2 .nH 2 O clusters (n=1-11) have absorption bands in UV-Vis region. Visualization of
appropriate MOs indicates that the strong absorption is due to an electronic transition
from the highest doubly occupied MO to the lowest singly occupied MO (σ→σ*) in all
these hydrated clusters as in for bare Cl •− 2 system. This suggests that micro hydration
does not change the bonding pattern in Cl •− 2 system. The optical absorption profiles for
each of the Cl •− 2 .nH 2 O systems (n=0-11) are generated using ten low lying excited states
and the UV-Vis spectra for Cl •− 2 and Cl •− 2 .10H 2 O systems are shown in Fig.5.3-I (a) and
(b), respectively. There is an excellent agreement between the experimental aqueous
phase optical absorption profile (see Fig.5.3-I c) and the present calculated one for
Cl 2 •− .10H 2 O cluster. 3,59
The calculated intensity is scaled with the measured molar
extinction coefficient value for Cl •− 2 (aq) following pulse radiolysis technique. It is worth
to mention that λ max values of the Cl •− 2 .nH 2 O clusters calculated applying Time
Dependent Density Functional Theory (TDDFT) are largely red shifted (~ 150 nm) in all
these hydrated clusters.
The aqueous UV-Vis spectra of other similar radicals (Br •− 2 and I •− 2 ) are also
studied. In these cases also the strong absorption is due to an electronic transition from
the highest doubly occupied MO to the lowest singly occupied MO (σ→σ*). The
simulated optical absorption profiles based on few low lying transitions for Br •− 2 .10H 2 O
and I •− 2 .8H 2 O hydrated clusters are also in excellent agreement with experimental
aqueous phase optical absorption profile.
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