AN AB INITIO MOLECULAR ORBITAL STUDY OF LOW LYING ELECTRONIC EXCITED STATES OF FeC (original) (raw)
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Electronic structure of compounds with Fe-C bonds
Journal of Molecular Structure: THEOCHEM, 1993
We present an ab initio study of the electronic structure of three compounds containing Fe-C bonds: CHXFeH, FeCHz and HFeCH. The geometries of several electronic states were optimised at the SCF or CASSCF level, with triple-zeta basis sets. Single point CI calculations allow the energy ordering of states of different symmetry and spin multiplicity to he assessed. The nature of bonding in the three compounds is discussed.
Time-Dependent Density Functional Theory Study of Fe 2 (CO) 9 Low-Lying Electronic Excited States
Journal of Physical Chemistry A, 2006
The molecular structures of the ground state and the first singlet excited state for diphenylboron analogs of Alq 3 [Ph 2 Bq where q is 8-hydroxyquinoline (QH)] and its three derivatives were optimized with the Density Functional Theory and ab initio "configuration interaction with single excitations" method, respectively. The frontier molecular orbital characteristics of Ph 2 Bq were analyzed systematically in order to study the electronic transition mechanism. Electronic and spectroscopic properties of complexes have been investigated with Time-Dependent Density Functional Theory, which indicates that the emissions of Ph 2 Bq and its derivatives originate from the electronic π → π * transitions within the QH ligands. That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand. Similar calculations were carried out for isolated QH and its three derivatives for comparison. We found that the highest occupied molecular orbital and the lowest unoccupied molecular orbital of Ph 2 Bq are similar to those of QH and their spectroscopic properties change similarly when they are substituted by the same group, which suggests that one can search possibility of a red or blue emission from Ph 2 Bq derivatives by analyzing QH and its derivatives.
2007
The potential energy curves have been calculated for the 59 lowest electronic states of the molecule NaCs including the spin-orbit effect within the range of 4.5a 0-20.0a 0 of the internuclear distance R. Using an ab initio method, the calculation is based on a nonempirical pseudopotentials which take into consideration the spin-orbit effect. Gaussian basis sets have been used for both atoms, and the spin-orbit effects have been taken into consideration. The spectroscopic constants have been calculated for 56 electronic states. The components of the spin-orbit splitting have been identified for the states ͑1,2,4͒ 3 ⌸. The comparison of the present results with those available in the literature shows a very good agreement.
A theoretical study of FeCN in the 6Δ electronic ground state
Journal of Molecular Spectroscopy, 2007
The three-dimensional potential energy and dipole moment surfaces for the electronic ground state 6 D of FeCN have been computed at the MR-SDCI + Q + E rel /[Roos ANO (Fe), aug-cc-pVQZ (C, N)] level of theory, where MR-SDCI means 'multi-reference single and double excitation configuration interaction' and ANO means 'atomic natural orbital'. Based on these potential energy and dipole moment surfaces, the spectroscopic parameters, rovibronic energies, structural parameters, vibrational transition moments, and the wavenumbers and intensities of selected rotation-vibration transitions have been calculated. The equilibrium structure is linear with r e (Fe-C) = 2.048 Å and r e (C-N) = 1.168 Å , and the zero-point averaged structure is bent with AEr(Fe-C)ae 0 = 2.082 Å , AEr(C-N)ae 0 = 1.172 Å , and AE\(Fe-C-N)ae 0 = 170(5)°. At all the MR-SDCI + Q and the size-extensive multi-reference averaged quadratic coupled-cluster (MR-AQCC) levels of theory, with and without relativistic correction E rel , that were employed in the present work, 6 D FeCN is predicted to be slightly more stable than 6 D FeNC. For example, the energy difference between the two isomers is approximately 150 cm À1 at the highest level of theory employed, MR-AQCC + E rel /[Roos ANO (Fe), aug-cc-pVQZ (C, N)] with zero-point energy correction. The electronic structure of 6 D FeCN has also been compared with that of 6 D FeNC. At present, no experimental spectroscopic data are available for 6 D FeCN. It is hoped that the present work will stimulate experimental investigations of this molecule.
The Journal of Chemical Physics, 2004
With several levels of multireference and restricted open-shell single-reference electronic structure theory, optimum structures, relative energetics, and spectroscopic properties of the low-lying 6 ⌬, 6 ⌸, 4 ⌬, 4 ⌸, and 4 ⌺ Ϫ states of linear FeNC and FeCN have been investigated using five contracted Gaussian basis sets ranging from Fe͓10s8p3d͔, C/N͓4s2 p1d͔ to Fe͓6s8 p6d3 f 2g1h͔, C/N͓6s5p4d3 f 2g͔. Based on multireference configuration interaction ͑MRCISDϩQ͒ results with a correlation-consistent polarized valence quadruple-zeta ͑cc-pVQZ͒ basis set, appended with core correlation and relativistic corrections, we propose the relative energies: T e (FeNC), 6 ⌬(0)Ͻ 6 ⌸ (2300 cm Ϫ1)Ͻ 4 ⌬ (2700 cm Ϫ1)Ͻ 4 ⌸ (4200 cm Ϫ1)Ͻ 4 ⌺ Ϫ ; and T e (FeCN), 6 ⌬(0) Ͻ 6 ⌸ (1800 cm Ϫ1)Ͻ 4 ⌬ (2500 cm Ϫ1)Ͻ 4 ⌸ (2900 cm Ϫ1)Ͻ 4 ⌺ Ϫ. The 4 ⌬ and 4 ⌸ states have massive multireference character, arising mostly from 11→12 promotions, whereas the sextet states are dominated by single electronic configurations. The single-reference CCSDT-3 ͑coupled cluster singles and doubles with iterative partial triples͒ method appears to significantly overshoot the stabilization of the quartet states provided by both static and dynamical correlation. The 4,6 ⌬ and 4,6 ⌸ states of both isomers are rather ionic, and all have dipole moments near 5 D. On the ground 6 ⌬ surface, FeNC is predicted to lie 0.6 kcal mol Ϫ1 below FeCN, and the classical barrier for isocyanide/cyanide isomerization is about 6.5 kcal mol Ϫ1. Our data support the recent spectroscopic characterization by Lei and Dagdigian ͓J. Chem. Phys. 114, 2137 ͑2000͔͒ of linear 6 ⌬ FeNC as the first experimentally observed transition-metal monoisocyanide. Their assignments for the ground term symbol, isotopomeric rotational constants, and the Fe-N 3 stretching frequency are confirmed; however, we find rather different structural parameters for 6 ⌬ FeNC:r e (Fe-N) ϭ1.940 Å and r(N-C)ϭ1.182 Å at the cc-pVQZ MRCISDϩQ level. Our results also reveal that the observed band of FeNC originating at 27 236 cm Ϫ1 should have an analog in FeCN near 23 800 cm Ϫ1 of almost equal intensity. Therefore, both thermodynamic stability and absorption intensity factors favor the eventual observation of FeCN via a 6 ⌸← 6 ⌬ transition in the near-UV.
Accurate ab initio calculations of the ground states of FeC, FeC+, and FeC
Chemical Physics, 2010
For the ground states of the diatomic carbide FeC(X 3Δ) and its ions, FeC+(X 2Δ) and FeC-(X 2Δ), we report on accurate multireference variational ab initio results employing augmented correlation consistent basis sets of quintuple cardinality. The dissociation energies and bond lengths are found to be D00=87+/-1, 95.2, and 84+/-1 kcal/mol at re=1.581, 1.556, and 1.660 A˚ for FeC, FeC+, and FeC-, respectively. All our final numbers are in agreement with the available experimental data.
First Principles Investigation of the Electronic Structure of the Iron Carbide Cation, FeC
Journal of Physical Chemistry A, 2005
We have studied 40 states of the diatomic iron carbide cation FeC + by multireference methods coupled with relatively large basis sets. For most of the states, we have constructed complete potential energy curves, reporting dissociation energies, usual spectroscopic parameters, and bonding mechanisms for the lowest of the studied states. The ground state is of 2 ∆ symmetry, with the first excited state (a 4 Σ -) lying 18 kcal/mol higher. The X 2 ∆ state displays a triple-bond character, with an estimated D 0 value of 104 kcal/mol with respect to the adiabatic products or 87 kcal/mol with respect to the ground-state fragments.
Theoretical investigation of iron carbide, FeC
The Journal of Chemical Physics, 2002
Employing multireference variational methods ͑MRCI͒, we have constructed full potential-energy curves for the ground state (X 3 ⌬) and forty excited states of the diatomic carbide, FeC. For all states we report potential-energy curves, bond lengths, dissociation energies, dipole moments, and certain spectroscopic constants, trying at the same time to get some insight on the bonding mechanisms with the help of Mulliken populations and valence-bond-Lewis diagrams. For the X 3 ⌬ state at the MRCI level of theory, we obtain a dissociation energy D e ϭ86.7 kcal/mol at a bond length r e ϭ1.581 Å. These values compare favorably to the corresponding experimental ones, D e ϭ91.2Ϯ7 ͑upper limit͒ kcal/mol and r e ϭ1.5924 Å. The first excited state ( 1 ⌬) is predicted to be 9.7 kcal/mol above the X-state as compared to an experimental value of 9.786 kcal/mol. Finally, Leung and co-workers 16 by laser infrared spectroscopy, they found the spin-orbit splitting between the X 3 ⌬ 2 and X 3 ⌬ 3 states to be 329.809 cm Ϫ1 .
The European Physical Journal B, 2010
We have studied the electronic structure of iron phthalocyanine (FePc) films at low temperature using electron energy-loss spectroscopy. The electronic excitation spectrum of FePc is rather complex and comprises both π-π * transitions of the phthalocyanine ligand and transitions that involve the Fe 3d orbitals. The C 1s core excitations provide so far unidentified information on the molecular orbitals. They demonstrate that the Fe 3d orbital with eg symmetry is energetically located in between the highest occupied and the lowest unoccupied ligand state and that it is not fully occupied.
First Principles Investigation of the Electronic Structure of the Iron Carbide Cation, FeC+
Journal of Physical Chemistry A, 2005
We have studied 40 states of the diatomic iron carbide cation FeC + by multireference methods coupled with relatively large basis sets. For most of the states, we have constructed complete potential energy curves, reporting dissociation energies, usual spectroscopic parameters, and bonding mechanisms for the lowest of the studied states. The ground state is of 2 ∆ symmetry, with the first excited state (a 4 Σ-) lying 18 kcal/mol higher. The X 2 ∆ state displays a triple-bond character, with an estimated D 0 value of 104 kcal/mol with respect to the adiabatic products or 87 kcal/mol with respect to the ground-state fragments.