Iron, atomic energy level

J. Sugar, C. Corliss Atomic energy levels of the iron-period elements Potassium through Nickel, Phys. Chem. Ref. Data 14, Suppl. 2 (1985)... 

Sugar, J. and Corliss, C., Atomic Energy Levels of the Iron Period Elements Potassium through Nickel, /. Phys. Chem. Ref Data, Vol.l4, Suppl. 2,1985. 

These measurements enabled us to find the shifts of the and lines of iron in the oxide relative to the corresponding lines of the pure element. The shifts of the two lines were of the order of 0.2 eV. The line shifted toward shorter wavelei hs and the line shifted toward longer wavelengths (Table 1). This was not in conflict with the current ideas on the changes in the positions of the atomic energy levels resultii from the conversion of a pure transition metal to a compound. 

In order to dissipate the recoil energy Mossbauer was the first to use atoms in solid crystal lattices as emitters and also to cool both emitter and absorber. In this way it could be shown that the 7-ray emission from radioactive cobalt metal was absorbed by metallic iron. However, it was also found that if the iron sample were in any other chemical state, the different chemical surroundings of the iron nucleus produce a sufficient effect on the nuclear energy levels for absorption no longer to occur. To enable a search for the precisely required absorption frequency, a scan based on the Doppler effect was developed. It was noted that a velocity of 102 ms-1 produced an enormous Doppler shift and using the same equation (7) it follows that a readily attainable displacement of the source at a velocity of 1 cms-1 produces a shift of 108 Hz. This shift corresponds to about 100 line-widths and provides a reasonable scan width. 

The Mbssbauer effect involves resonant absorption of y-radiation by nuclei in solid iron oxides. Transitions between the I = Y2 the I = 72 nuclear energy levels induce resonant absorption (Fig. 7.4). A Mbssbauer spectrum is a plot of the transmission of the rays versus the velocity of their source movement of the source ( Co for iron compounds) ensures that the nuclear environments of the absorber and the source will match at certain velocities (i.e. energies) and hence absorption takes place. In the absence of a magnetite field the Mbssbauer spectrum consists of one (if the absorbing atoms are at a site of cubic symmetry) or two (symmetry distorted from cubic) absorption maxima. When a static magnetic field acts on the resonant nuclei, this splits the nuclear spin of the ground state into two and those of the ex-... 

Fig. 11-8.—Values of energy levels of carbon atoms and iron atoms, as determined by spectroscopic methods. The unit of energy used in the scale at the left is the electron volt.

It was pointed out in Section 4-2 that the configuration sp8, which has promotion energy about 200 kcal/mole relative to the ground configuration 2s22p2, is the basis of the quadrivalent state of the carbon atom and is shown by quantum-mechanical calculations for methane to contribute about 49 percent to this valence state. Now let us consider the iron atom, for which spectroscopic energy levels are shown on... 

Other Bis-cyclopentadienyl Compounds.—It is interesting to give similar accounts of other neutral molecules like ferrocene, where the central iron atom is replaced by Co, Ni, Cr or other atoms of the transition elements. The energy level diagram will not be veiy different from Fig. 11 in all these cases, and we may treat the molecules by adding, or subtracting the requisite number of electrons. 

Assuming that the structure shown in Fig. 15 is valid, one can draw some conclusions as to the characters of the iron-orbitals in the "spin-coupled model. Since the symmetry around the iron is tetrahedral, the d and dx2-y2 orbital are more ionic than the tg orbitals which must be covalent as the ligands are sulfur atoms. There are several important consequences of this conclusion 1. The energy level scheme is based on crystal-field approximations and therefore can be considerably in error. 

For these samples, matrix corrections were not made. The matrix effects are most severe at the lower energy levels and are considered to be of almost negligible importance for elements having an atomic weight greater than that of iron. Thus, concentrations of Al, Si, S, and Cr may be in error by up to 50% of the amount present because of matrix effects and relatively poor counting statistics. All other reported elements are estimated to be accurate to within 10% of the correct values. 

The procedure for calculating energy level diagrams by the self-consistent field Xa scattered wave (SCF-Xa-SW) method is as follows (Sherman, 1984, 1991). An octahedral cluster such as [FeO6]10 is partitioned into a set of (overlapping) spheres centred about divalent iron and each oxygen atom, and these are surrounded by an outer sphere. Within each atomic sphere the one-electron Schrodinger equation... 

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