Diatomic molecules, correlation diagrams

Figure 9.2. Correlation diagram for second-row diatomic molecules. The column on the left shows orbitals for the united atom, those on the right those of the separated atoms.

We are discussing our manner to calculate the total energy for small molecules within the DV-Xa approximation by using only the monopol part of the potential in the solution of the Poisson equation. A discussion of the relativistic effects, including our results for heavy diatomic molecules, is followed by remarks on the choice of the exchange-correlation potential together with our results of calculations on molecules for the element 106 and their chemical interpretation. We conclude with results on very heavy correlation diagrams for collision systems with a united Z above 110. 

E.E.Nikitin and R.N.Zare, Correlation diagrams for Hund s coupling cases in diatomic molecules with high rotational angular momentum. Mol. Phys. 82, 85... 

The abscissas of the correlation diagrams can be quantified. The quantification is thus far only an ex post facto device with power to classify but not yet to predict. It does not yet have a microscopic interpretation. Nevertheless it satisfies the needs of a theory of the equilibrium behavior of melting and freezing of clusters. Only the existence and not the definition of the nonrigidity parameter or the details of its origins is used in stage 2. However, we make a brief aside here to explain the definition in order to clarify just what information it carries. To understand the order parameter y (not to be confused with the surface tension), it is useful to examine how nonrigidity is traditionally characterized in diatomic and linear, particularly triatomic molecules. For... 

FIGURE 6.10 Correlation diagram for first-period diatomic molecules. Blue arrows indicate the electron filling for the H2 molecule. All of the atomic electrons are pooled and used to fill the molecular orbitals using the aufbau principle. In the molecules, electrons are no longer connected to any particular atom. 

FIGURE 6.16 Correlation diagrams for second-period diatomic molecules, (a) Correlation diagram and molecular orbitals calculated for N2. (b) Correlation diagram and molecular orbitals calculated for F2. 

FIGURE 6.19 Correlation diagram for heteronuclear diatomic molecules, AB. The atomic orbitals for the more electronegative atom (B) are displaced downward because they have lower energies than those for A. The orbital filling shown is that for (boron monoxide) BO. 

Construct correlation diagrams for diatomic molecules formed from second-and third-period main-group elements. From these diagrams, give the electron configurations, work out the bond orders, and comment on their magnetic properties (Section 6.2, Problems 17-30). 

The bond length of the transient diatomic molecule CF is 1.291 A that of the molecular ion CF is 1.173 A. Explain why the CF bond shortens with the loss of an electron. Refer to the proper MO correlation diagram. 

FIGURE 8.6 Orbital correlation diagram for homonuclear diatomic molecules of the transition metals... 

Figure 11.20 MO occupancy and molecular properties for B2 through Ne2- The sequence of MOs and their electron populations are shown for the homonuclear diatomic molecules in the p block of Period 2 [Groups 3A(13) to 8A(18)]. The bond energy, bond length, bond order, magnetic properties, and outer (valence) electron configuration appear below the orbital diagrams. Note the correlation between bond order and bond energy, both of which are inversely related to bond length.

We can extend the method to heteronuclear diatomics with relative ease. Since the heteronuclear molecule does not have the nuclear exchange symmetry the g and u character is lost, but the rest of the notation remains the same. The correlation diagram becomes more complicated because of the difference in energies of the electron on the two different separated atoms. It is worth noting that isoelectronic species such as N=N, C=0,... 

Diatomic Molecules as Possible Diagnostic Reagents and the Use of Correlation Diagrams. Since the primary reactions of polyvalent atoms are expected to form reactive intermediates, the most general approach to characterizing these primary reactions is to pick substrates whose reactions are most likely to convey information about the electronic states of the reacting atom and the geometry of its attack on the substrate. 

If the electronic states of the primary reaction products from a recoiling atom and a diatomic molecule can be determined, then adiabatic correlation diagrams could be used to deduce the electronic state of the reacting recoil atom, or the symmetry of attack, or both. 

A useful principle in drawing orbital correlation diagrams is the noncrossing rule, which states that for MO correlation diagrams of many-electron diatomic molecules. 

Fig. 39. Correlation diagram for the individual electrons in diatomic molecules with equal nuclei.

Fig. 3.5 displays Mulliken s [2] generalized orbital correlation diagram for homonuclear diatomic molecules, which has been of seminal importance for the elucidation of the electronic structure of molecules. Only the atomic levels n = 1,2 have been included on its right on the left, the orbitals of the united atom have been extended sufRciently that all of the necessary correlation lines can be drawn. The energetic spacing of the AOs is purely schematic, their order on the left being that common to silicon and sulfur, the united atoms corresponding to N2 and O2. The abcissa, is - of course - quite non-linear. 

Diatomic molecules are necessarily linear, but a triatomic molecule can be either linear like CO2 and HCN or bent like SO2 and H2O. Mulliken s correlation diagram procedure was extended to tri- and tetraatomic molecules by Walsh [1], who promulgated a set of simple but remarkably viable [2, 3, 4] rules for predicting whether or not a molecule will remain linear, from the effect of the departure from linearity on the energy of its occupied molecular orbitals. 

For the homonuclear diatomic molecule Be2, give the MO configuration and bond order for the ground state and first excited state, based on the correlation diagram as the values of R approach (a) the separated atom limit and... 

Homonuclear diatomics of heavier elements tend to lie closer to the separated atom limit of the correlation diagram (Fig. 7.2). Based on the dashed line representing O2 in this figure, what neutral, homonuclear, diatomic molecule would be the first to have a filled 8 molecular orbital in its groimd state, and how many electrons does it have ... 

The Ne2 molecule dissociates at room temperature. Using the correlation diagram for homonuclear diatomics... 

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