Spin-orbit coupling strength

The magnitude of the total spin-orbit coupling strength can change dramatically as a function of biradical conformation (Carlacci et al., 1987). The through-space part can be roughly approximated by... 

The three sublevels of the triplet couple to the So singlet to different degrees, dictated by the singlet-triplet separation and by the matrix elements f/f , and respectively. The nuclear spin states are immaterial. Often, it is assumed that the relaxation between the three levels is rapid, or that all three are initially populated more or less equally, and the total spin-orbit coupling strength of the So state is then defined as +... 

In this report the symbol a is used (i) for the spin-orbit coupling strength [in which connection it nearly always occurs as part of the intermediate coupling parameter aJK (Sect. 3)] (ii) as the interaction radius in penetrability calculations and reduced widths % l Ma) (Sect. 9) and (hi) as the bombarding particle in the reaction X (ab) Y (Sect. 6). These meanings are sufficiently distinct to avoid confusion. 

In ordinary optical absorption there are two components associated with intraband transitions (Drude component) and interband transitions, respectively. A similar situation is encountered in magneto-optical spectroscopy. Of special interest is the interband component which is related to the joint density of states. The intensity of the magneto-optical transitions is proportional to the product of spin-orbit coupling strength and net electron-spin polarization of states excited by the incident light (Erskine and Stern, 1973). 

Under conditions of rapid relaxation among the three triplet levels, the singlet-triplet coupling is frequently characterized by the "total spin-orbit coupling strength" for the Sj state, defined by... 

The vector nature of the addition of the contributions from the individual nuclei ac in the construction of the total spin-orbit coupling vector is important. It is often assumed that introduction of a heavy atom into a molecule cannot but increase the spin-orbit coupling strength (the "heavy-atom effect"). This is clearly wrong. If the additional contribution is a vector that is opposed to the resultant of those already present, the value of SOCi may actually decrease upon the introduction of a heavy atom. We believe to have identified an experimental case of such behavior recently [18]. 

Some more recent calculations [28], based on careful consideration of the effect of mass asymmetry on the fission barrier and a reduced spin-orbit coupling strength, have indicated that the Z = 114 shell effect is not very large. These calculations do confirm the existence of a shell atN = 184, but also suggest less stability for species with N < 184 that is, the island of stability has a cliff with a sharp drop-off for N < 184. If these considerations are correct, it would become considerably more difficult to synthesize and detect the superheavy elements (defined as those elements stabilized by spherical closed-nucleon shells). A premium would be placed on produdng a nucleus with N = 184 or, very close to this, N = 183, in order that it might have a half-life sufficiently long to make it detectable. 

---