Spin-orbit coupling conical intersections

Spin multiplicity, permutational symmetry, dynamic Jahn-Teller and geometric phase effects, 706-711 Spin-orbit coupling conical intersections ... 

The initial systematic introduction of the model into photochemistry is now nearly two decades old [2-5]. More recently, the model has been elaborated [1,6,7] and its utility for the prediction and rationalization of geometries at which Sq - conical intersections occur has been recognized [1,6-8]. While most of the standard expositions have concentrated on the orbital and configuration (in this case, geminal) space as opposed to the spin space part of the electronic problem, one of the two early reviews treated spin-orbit coupling as well and formulated useful general rules [2] which have since found support in ab initio calculations [9]. 

Schuurman MS, Weinberg DE, Yarkony DR (2007) On the simulation of photoelectron spectra in molecules with conical intersections and spin-orbit coupling the vibronic spectrum ofCHsS. J Chem Phys 127 104309... 

Conical intersections usually appear in the Jahn-Teller form in inorganic transition metal complexes because the high symmetry of such complexes allows for this symmetry-required type of conical intersection. For example, studies of complexes of metals with carbonyls revealed that conical intersections facilitate the photodissociation of CO. It should be noted, however, that a sufficient amount of work has not been done yet in this area to reveal whether accidental conical intersections exist and what role, if any, they play in photodissociation. As a result of the larger spin-orbit coupling in transition metal systems, there exists a higher probability for spin-forbidden transitions (intersystem crossing) than in nontransition metal systems. Matsu-naga and Koseki have recently reviewed spin-forbidden reactions in this book... 

Using the conditions in Eqs. [47]-[49] and perturbation theory near a conical intersections, algorithms based on the Lagrange multipliers method were developed. These techniques can locate conical intersections when the spin-orbit coupling is included in the Hamiltonian with perturbative methods. ... 

Figure 7 Energy level diagram of the intersecting states in H2 -I- OH (a) at the nonrelativistic conical intersection point without spin-orbit coupling (b) at the nonrelativistic conical intersection point with spin-orbit coupling (c) at the new relativistic conical intersection.

Figure 8 Energy of the minimum energy point on the seam for the S — II conical intersection of H2 + OH with, and without, spin-orbit coupling. The numbers in the diagram adjacent to the molecules are computed bond lengths in A.

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