H. Nakai et al., ELECTRONIC-STRUCTURES OF MOF6 AND MOOF4 IN THE GROUND AND EXCITED-STATES - A SAC-CI AND FROZEN-ORBITAL-ANALYSIS STUDY, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 102(11), 1998, pp. 2033-2043
The symmetry-adapted-cluster (SAG) and SAG-configuration interaction (
SAC-CI) many-body theories have been applied to calculate, within the
all-electron ab initio Hamiltonian, the singlet ground and excited sta
tes of MoF6 and MoOF4. Chemical bonding and electron correlation are q
uite important to reduce the formal charge of electrostatic Mo-ligand
bonds in both ground and excited states. The calculated excited states
are all characterized as electron-transfer excitations from ligands t
o molybdenum, reducing the ionicity of the Mo-F bonds. For MoF6, we as
sign the energetically lower three peaks to dipole-allowed electronic
transitions to the T-1(1n), excited states, consistently with the calc
ulated oscillator strengths, and at variance of the previously propose
d assignments. The fourth and fifth peaks, having very weak intensity,
have been tentatively assigned to the dipole-forbidden 2(1)E(g) and 4
(1)T(2g) excited states, respectively. The experimental excitation ene
rgies and intensities are well reproduced by the present calculations.
The maximum discrepancy (0.35 eV) of the calculated excitation energi
es occurs for the first peak. Chemical bondings of MoOF,I in the groun
d and excited states, although exhibiting great reductions of the ioni
city, are more ionic than those of MoF6. For the visible-UV spectrum o
f MoOF4, we assign the two experimental peaks to dipole-allowed transi
tions to the E-1 excited states. The present assignments of the observ
ed electronic transitions based on the accurate SAC-CI calculations sh
ould be more reliable than the previous ones. We further used the froz
en-orbital-analysis (FZOA) method in order to understand and rationali
ze the energy orderings and splittings for the excited states having t
he same excitation nature. We confirm that the FZOA method is very sim
ple and useful to examine and explain the origin of the orderings of t
he excitation levels. Some relationships on the orderings and splittin
gs presented here should be of general applicability to any systems.