Sextet state

Figure 6. Calculated potential energy curves for sextet states of FeO. The ground electronic Slate and excited states accessible by allowed electronic transitions from the ground state are shown. Points are calculated using TD-DFT at the B3LYP/6-311G(d,p) level. Sohd hnes are S states and dashed lines are II states, the vertical dashed hne indicates for the ground state. The experimental value of the dissociation energy is also diown for reference.

Table 13-10. Computed binding energies of FeO+ and [Fe(H20)]+ (D0 with respect to atomic and molecular sextet states) and overall reaction energies for three examples [kcal/molj. 

The spectrum of [MnBr(Meetren)]Br (8) (Fig. 26) shows very weak bands in the region 15—32 kK (e 0.4—1.2) which are to be attributed to spin-forbidden transitions from the ground sextet state to the first quartet levels. Dr. j0rgensen kindly provided to the author information about the energy levels of manganese(II) in trigonal bipyramidal chromophores. 

This minute amount of mixing of the quartet and sextet states leads to a very small intensity for the sextet-quartet transition, as, strictly speaking, the AS = 0 selection rule is no longer violated. A more detailed discussion on the spin-orbit interaction in complexes is given in Section 8.7. 

For low-spin octahedral d, the ground state is T2g, that is, (t2g). One hole in t2g is analogous to octahedral d or tetrahedral d . Thus Figure 8 is apphcable, with one spin-allowed d-d transition, "T2g-"Eg, whose energy is equal to Aq. There are quartet excited states, plus the unique sextet state Aig. The vast majority of octahedral Mn° compounds are high-spin iron(ni) complexes have larger Aq values and low-spin ground states are more common, for example, in [Fe(CN)6] and [Fe(bipy)3] +. 

Doublet state Quartet state Sextet state ... 

The sextet state configuration is unique. The choice of the lowest energy configuration for the doublet and quartet states was confirmed by comparisons of the relative energies of various quartet and doublet configurations, obtained by assignment of unpaired electron(s) to different iron d orbitals, in some representative complexes. It is also corroborated by a recent detailed study of... 

For the dicyano and azide-pyridine complexes, our calculated results indicate that in each case a S = 1/2 spin state is the lowest energy state with the quartet and sextet states much higher in energy. The observed effective magnetic moments (Table I) of both... 

For MMB (Table V), the sextet state is the lowest energy state for the neutral imidazole ligand with the quartet and doublet states and 8 kcal/mol higher in energy. In contrast to CCP where regularization of the porphyrin ring to symmetry had little... 

The calculated relative spin state energies for CAT (Table V) at the crystal geometry shows that the the sextet state is the most... 

In the case of MoO no experimental or other theoretical data are available by now. The ground state of MoO+ comes from the dT ionization, the second one is the as ionization effect, both render well-defined 4E" and 4II states. The interpretation of ionizations in the /3 manifold is even more complicated than for the VO molecule. The lowest energy sextet state is again the 6II "shake-up" state coming from /3-zr ionization combined with the a os - d transition. Unfortunately, the direct /8-ir hole state gives rise to three energy terms and must be taken with caution. The fi-o ionization would lead to the well-defined 6I1 state, it is, however, the second state of this symmetry lying very close to the "shake-up state and thus inaccessible by the present calculations. 

Table 4 shows the results for the best LSD potential of Vosco, Wilk and Nusair [12] (DFT/L) compared with experiment [21] as well as with other theoretical extensive configuration interaction and coupled-pair functional method [23], where available. Four quintets, one doublet and two sextet states are included in the table. The overall impression which arises from inspection of numbers is that the LCGTO-LSD method works for vanadium oxide even better than could be expected for such a difficult example. Equilibrium bond distances approach the experimental values very closely, similarly to other spectroscopic constatnts even though they have been obtained from a very simple polynomial fit to an approximate, few-point curve. As a rule, the... 

Our investigations on the 2 A state can provide some help in positioning the part of the spectrum coming from doublet states, known experimentally from rotational analyses or perturbations but whose absolute energies were only approximately evaluated [21]. The sextet states of VO are described only approximately since the potential energy curves are very flat and more points would be desirable in order to perform more exact analysis. Nevertheless, their positions and geometric properties are consistent with a simple picture given by a qualitative molecular orbital scheme. 

Low-lying states of FeH have been studied both experimentally and theoretically by many groups, and it is now well established that the ground state is a quartet (X A), lying 0.24 eV below the lowest sextet state (a A). An extensive theoretical study of the plethora of low-lying states of various symmetries has been presented by Langhoff and Bauschlicher [18]. 

Calculated data on CN, SiN and SiP from Refs. 76 and for CP as well as for all sextet states stem from Ref. 79. 

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