CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

7.3.3. Vertical Detachment Energy
Vertical detachment energy (VDE) of I •− 2 .nCO 2 (n=1-8) clusters are reported by
Neumark and co-workers. 48 Vertical detachment energy (VDE) is the energy required to
remove an electron from the anionic solvated clusters. VDE of the solvated clusters,
I •− 2 .nCO 2 can be defined by the relation:
VDE n = E[I •− 2 .nCO 2 ] - E s [I 2 .nCO 2 ],
where E[I •− 2 .nCO 2 ] is the energy of the optimized I •− 2 .nCO 2 cluster and E s [I 2 .nCO 2 ] is the
single point energy of the I 2 .nCO 2 obtained by removing the extra electron from the
optimized I •− 2 .nCO 2 cluster. The VDE for the minimum energy structures (most stable
structure) of the cluster, I •− 2 .nCO 2 (n=1-8) is calculated following post Hartree-Fock
second order Moller-Plesset (MP2) perturbation theory with 6-311+G(d) set of basis
functions (for I 6-311G(d) basis set is taken). The VDE values calculated without and
with spin-orbit coupling are tabulated in Table 7.1. The variation of VDE with the size of
the cluster (n) is shown in Fig. 7.2-II (a) and II (b), respectively without and with spinorbit
coupling (SOC) with relativistic corrections. 80 It is clearly seen that the VDE values
is blue-shifted with increasing cluster size and this is consistent with the previous report
(the experimental data is also shown in Fig. 7.2-II-c). 48
Increasing VDE with size
signifies that the stability of the neutral cluster decreases with size. The calculated values
of VDE and the variation of present theoretical values on VDE of solvated clusters with
size is in excellent agreement with the VDE value corresponding to the X band measured
by Neumark and coworker (see Table 7.1). 48 The X band is only surviving band for
highest cluster (n=8) in their study. It is worth to mention that the weighted average VDE
is also calculated for the I •− 2 .8CO 2 cluster (taking 6 minimum energy structures) and no
116