Hund’s case

When the molecule is not in a S state there is an interaction between the rotation of the molecule and S and/or L, and the details of coupling the angular momenta are involved. Most nonsinglet molecules with electronic orbital angular momentum A = 0 obey Hund s case (b) coupling. In Case (b), the electronic orbital angular momentum combines with the nuclear orbital angular... 

Figure 7.16 (a) Hund s case (a) and (b) Hund s case (c) coupling of orbital and electron spin... 

Changes in the degeneracy patterns between, for example, Hund s cases (a) and (c) can be attributed to monodromy. 

Most molecules with A>0 obey Hund s case (a). Here, the axial components of electronic orbital angular momentum (Ah) and of electronic spin angular momentum (2fc) combine to give a resultant axial component of total electronic angular momentum (A + 2)fi. The quantum number ft is defined as (Section 1.19)... 

E. W. Schlag It simply means that the electron is the slowest particle compared to the more rapid nuclear motions. For this reason, each rotation has its own Rydberg series. This is referred to typically as an inverse BO representation, similar to a Hund s case d. 

Recent work on these systems includes Cl2, Br2, and several of the interhalogen molecules. The results can be summarized in terms of the potential curves in Figs. 3 and 4. The excited electronic states of the halogens are described in Hund s case c coupling, so that spin is not a good quantum number, and reasonably strong... 

Let the diatomic (or linear) molecule satisfy the conditions for the Hund s case (a) coupling scheme (see Section 1.2, Fig. 1.3(a)), where the electronic orbital and spin angular momenta are coupled with the internuclear axis. The magnetic moment which is directed along the internuclear axis and corresponds to the projection Cl of the total angular momentum J upon the internuclear axis, has the value... 

Fig. 4.24. Vector scheme for the interaction of momenta of a diatomic molecule in a magnetic field in Hund s case (a) coupling scheme. The frequency u)q of nutation of fl and (j,q around J considerably exceeds the frequency u>j of the precession of J around B.

The case of intermediate coupling of momenta (between Hund s cases (a) and (6)), as well as that of breaking weak field approximation axe discussed in [294]. The molecular (/-factors for Hund s case (c) coupling are discussed in [92, 364]. 

For a linear molecule, only the 2 component of JTso is involved in the evaluation of diagonal matrix elements. In a Hund s case (a) basis,161 the fine-structure parameter Ae at the equilibrium geometry Qe can be obtained from... 

Typically, Hund s case (b)161 applies to molecules with A = 0, to which spin-orbit effects do not contribute in first order. For states with a nonzero A value and a rotational parameter Bv of the same order-of-magnitdue as the spin-orbit parameter Av, rotational coupling cannot be neglected. In this case, it... 

The strong coupling limit, Hund s case (c)161, cannot be dealt with in first order. Rather, it requires the inclusion of higher-order (at least second-order) spin-orbit coupling in the calculations. 

Kramers-Type Splitting in the X2II and a4S States of CH and CD Calculated in a Hund s Case (a) Basis. 

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