  Na2IrO3 (NIO) is known to be a spin-orbit (SO) driven j=1/2 pseudo-spin
Mott-Hubbard (M-H) insulator. However, the microscopic origin of the
pseudo-spin state and the role of local structural distortions have not been
clearly understood. Using a combination of theoretical calculations and x-ray
spectroscopy, we show that the energetics in the vicinity of Fermi level (EF)
is governed by SO interactions, electron correlation and local octahedral
distortions. Contrary to the earlier understanding, here we show that the j=3/2
and 1/2 pseudo-spin states have admixture of both t2g and eg characters due to
local structural distortion. Reduction of local octahedral symmetry also
enables Ir 5d- O2p hybridization around the EF resulting in a M-H insulator
with enhanced charge transfer character. The possibility of Slater insulator
phase is also ruled out by a combination of absence of room temperature DoS in
valence band spectra, calculated moments and temperature dependent
magnetization measurements.
