The vibrational spectrum of FeO2+ isomers (original) (raw)
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The vibrational spectrum of FeO2+ isomers—Theoretical benchmark and experiment
The Journal of Chemical Physics, 2014
Infrared photodissociation is used to record the vibrational spectrum of FeO 2 + (He) 2-4 which shows three bands at 1035, 980, and 506 cm −1 . Quantum chemical multi-reference configuration interaction calculations (MRCISD) of structures and harmonic frequencies show that these bands are due to two different isomers, an inserted dioxo complex with Fe in the +V oxidation state and a side-on superoxo complex with Fe in the +II oxidation state. These two are separated by a substantial barrier, 53 kJ/mol, whereas the third isomer, an end-on complex between Fe + and an O 2 molecule, is easily converted into the side-on complex. For all three isomers, states of different spin multiplicity have been considered. Our best energies are computed at the MRCISD+Q level, including corrections for complete active space and basis set extension, core-valence correlation, relativistic effects, and zero-point vibrational energy. The average coupled pair functional (ACPF) yields very similar energies. Density functional theory (DFT) differs significantly from our best estimates for this system, with the TPSS functional yielding the best results. The other functionals tested are BP86, PBE, B3LYP, TPSSh, and B2PLYP. Complete active space second order perturbation theory (CASPT2) performs better than DFT, but less good than ACPF. © 2014 AIP Publishing LLC.
The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1. The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ. The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
Vibrational Spectroscopy of Fe3(+)(CH4)n (n=1-3) and Fe4(+)(CH4)4
The journal of physical chemistry. A, 2017
Vibrational spectra are measured for Fe3+(CH4)n (n=1-3) and Fe4+(CH4)4 in the C-H stretching region (2650-3100 cm-1) using photofragment spectroscopy, monitoring loss of CH4. All of the spectra are dominated by an intense peak around 2800 cm-1 which is red shifted by ~120 cm-1 from free methane. This peak is due to the symmetric C-H stretch of the η3 hydrogen-coordinated methane ligands. For clusters with three iron atoms, the peak becomes less red shifted as the number of methane ligands increases. For clusters with one methane ligand per iron atom, the red shift increases in going from Fe2+(CH4)2 (88 cm-1) to Fe3+(CH4)3 (108 cm-1) to Fe4+(CH4)4 (122 cm-1). This indicates increased covalency in the binding of methane to the larger iron clusters and parallels their increased reactivity. Density functional theory calculations, B3LYP, BPW91 and M11L, are used to identify possible structures and geometries and to predict the spectra. Results show that all three functionals tend to over...
Electronic structure, vibrational spectrum and photochemistry of the Fe+H2 system
Chemical Physics, 1992
We present an ab initio study of the electronic structure of the Fe + Hz system, based on the CIPSI and CASSCF methods. The main points addressed in this paper are the nature of the electronic states of FeH2, its equilibrium geometry and the attribution of the observed vibrational bands. The latter two problems are the object of controversial interpretation of the experimental data: our conclusion is that the molecule is linear in the ground quintet state, and the symmetric stretching band cannot be detected in the IR spectrum. In order to clarify the photochemistry of the Fe+ HZ system, we have determmed potential energy curves for the insertion of the iron atom in the H-H bond, in the ground and several excited states origmating from Fe 5D( 3d64s2), 'F( 3d74s), 'P( 3d74s), 'D"( 3d64s4p), 'F"( 3d64s4p) and 'PO( 3d64s4p).
The Journal of Chemical Physics, 2003
The resonance enhanced ͑1ϩ1͒ photodissociation spectra of the ͑8,0͒ and ͑9,0͒ bands of the 6 ⌸ 7/2 ← 6 ⌺ ϩ system of FeO ϩ have been recorded. From a rotational analysis, the rotational parameters for the 6 ⌺ ϩ ground state of FeO ϩ have been obtained for the first time. The rotational constant B 0 ϭ0.5020Ϯ0.0004 cm Ϫ1 is derived, giving r 0 ϭ1.643Ϯ0.001 Å. Other molecular parameters determined for the 6 ⌺ ϩ ground state are the spin-spin coupling constant, ϭϪ0.126Ϯ0.006 cm Ϫ1 , and the spin-rotational coupling constant, ␥ϭϪ0.033Ϯ0.002 cm Ϫ1 . The assignment of the upper state as 6 ⌸ 7/2 is based on the characteristic appearance of the band and on time-dependent density functional ͑TD-DFT͒ calculations performed on FeO ϩ . The reliability of the TD-DFT method in the prediction of excited states of FeO ϩ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.
Organometallics, 2001
A theoretical study of the structural versatility of the di-iron carbonylate, [Fe 2 (CO) 8 ] 2-, and of its adducts with electrophiles is presented. The geometries of three energy minima and four transition states of [Fe 2 (CO) 8 ] 2have been characterized, and the relative energies of several alternative structures have been evaluated. The calculated vibrational spectra in the Fe-Fe and the CtO stretching regions are discussed for the three isomers, and a good correlation between the Fe-Fe stretching force constant and the Fe-Fe bond distance is found for both theoretical and experimental data. The effect of the orientation of the terminal ligands on the Fe-Fe bond and the rearrangement of such ligands by the formation of adducts with electrophiles are also addressed. a Abbreviations: im) N-methylimidazole; lut) N-methyllutidinium; py) pyridine.
Journal of Chemical Theory and Computation, 2012
The photoelectron spectrum of FeO 2 − has been assigned by performing geometry optimizations at the CASPT2 and RCCSD(T) levels of computation. All relevant states are found to possess floppy C 2v geometrical structures as the Renner-Teller splittings of the linear states are extremely small and the corresponding energy barriers for the OFeO bond angle inversions are calculated in the range of a few hundred wavenumbers. In this sense, the description of the electronic structure in terms of the D ∞h point group is acceptable, and the experimentally proposed linear structure for FeO 2 − is theoretically confirmed. High accuracy single-point multireference RASPT2 and single-reference RCCSD(T) calculations support a 2 Δ g as the ground state of the anion, even though the energy differences between the 4 Π g and 6 Σ g + states are smaller than 0.2 eV. After this identification of the doublet ground state, the photoelectron spectra of FeO 2 − could be assigned in all aspects. The 2 Δ g → 3 Δ g ionization appears to be at the origin of the X band at 2.36 eV, while the A band at 3.31 eV should be ascribed to the 2 Δ g → 3 Σ g + ionization. This assignment is substantiated by Franck−Condon factors for which BP86 optimized geometries and harmonic vibrational frequencies were employed. Indeed, no pronounced vibrational progression should be observed since both bands involve electron detachments out of nonbonding mainly 3d iron molecular orbitals.