## Ab initio quasirelativistic calculations on excited states of
OsO4 and IrO4+

**A.Dement'ev, A. Zaitsevskii, Yu. Kiselev**

First V.A.Fock Meeting on Quantum and Computational Chemistry,
Novgorod, 1998,No.62

**ABSTRACT**. Ab initio calculations on several low lying excited
electronic states of the OsO4 molecule and the isoelectronic
IrO4+ are performed within the quasirelativistic effective core
potential approach. A series of different contracted gaussian
basis sets rangnig from double zeta to (9s7p6d2f)/ [6s5p4d2f]
Os,Ir,(5s5p2d)/[3s3p2d] O are employed. The geometry
optimisation of the ground states was carried out at the
CASSCF level. The excitation energies are obtained by the
multipartitioning perturbation theory second-order calculations
and the difference- dedicated CI technique; in the latter case,
the CI space comprised ca. 105 numerically selected 'semiactive'
excitations of CAS-like functions. The lowest allowed excitation
from the ground state is identified with the transition to 1T2
state which is dominated by the promotion of an electron from
the 1t1 (essentially ligand-localised) MO to the 2e one arising
from the d AO of the central atom. The corresponding transition
energy in OsO4 is estimated to be 34575 cm-1; this value is in
excellent agreement with the experimentally observed energy
35000 cm-1 The spin-orbit splitting for all the states mentioned
above are found to be rather small.

Coordination Chemistry Laboratory