Spin-Orbit Coupling and Intersystem Crossing in Biradicals

SPIN-ORBIT COUPLING AND INTERSYSTEM CROSSING IN BIRADICALS 

The theory of spin-orbit coupling in organic biradicals essentially started in 1972 with the analysis by Salem and Rowland [7] performed for the 2-in-2 model of biradical electronic structure (active space tow electrons in two orbitals, also known as the 3 x 3 Cl model). A fair amount of theoretical work on SOC in 

Ab initio determinations of SOC in carbene (1) have been carried out for three bond angles (0 = 90, 112 and 135°) by McKellar et al. [27J using SCI and SDCI wave functions and by Vahtras et al. [19] for the equilibrium geometry employing a multiconfiguration linear response (MCLR) approach. Both sets of calculations are based on the full coupling operator with the 

In Table 1 ab initio values are compared to our results, which are seen to be some 10 cm too large. The reason for this discrepancy can be seen in the fact that the two-electron part of the spin-orbit coupling operator, which was retained 

Ethylene SOC values in cm from different methods for torsion ( j)) of the double bond 

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