Spin-orbit effects ionization potentials

Although adiabatic correlation arguments [10] could, in principle, be used to understand the observed spin-orbit effects, such considerations have been shown [119-123] to be poor predictors for the product electronic state branching in chemiluminescent alkaline earth reactions. Because of the relatively low ionization potentials of the excited alkaline earth atoms, their reactions proceed by charge transfer to an ionic surface [116]. As the reactants approach but before charge... 

Another important effect due to the spin-orbit coupling comes into play whether the upper ionic core is specifically involved or not. This is because the excitation dynamics is very sensitive not only to the ionization potential or binding energy of the active electron but also to m, the projection of the orbital angular momentum along the polarization axis. Since spin-orbit terms are not... 

Equations for the Fock space coupled cluster method, including all single, double, and triple excitations (FSCCSDT) for ionization potentials [(0,1) sector], are presented in both operator and spin orbital form. Two approximations to the full FSCCSDT equations are described, one being the simplest perturbative inclusion of triple excitation effects, FSCCSD+T(3), and a second that indirectly incorporates certain higher-order effects, FSCCSD+T (3). 

The ionization potentials and electron affinities of the atoms H, C, N, O and F have been computed by means of coupled-cluster methods using doubly augmented correlation-consistent one-electron basis sets in conjunction with explicitly correlated Slater-type geminals. Excitations up to the level of connected quintuples have been accounted for, and all orbitals in the core and valence shells have been correlated. Relativistic effects (spin-orbit as well as scalar) and diagonal Born-Oppenheimer corrections have been included. 

Figure 1.14 Ionization potential in various approximations. Note that the spherical sawtooth behavior is completely destroyed after allowing for spheroidal distortions. Originally it was believed that the strong odd-even alternation was related to the spin of the electrons. But, as shown first by the first author [29], it is a kinematic orbital effect. Reproduced with permission from Reference [29]. Copyright 1988 by the American Physical Society...

The third critical point is the choice of the appropriate electronic structure method to treat the species in gas phase. The change of electronic configuration from the oxidized to the reduced species implies that electronic correlation effects are different and that spin-orbit coupling is likely to contribute differently for the two species. Most studies rely on DFT using either the PBE functional, a hybrid functional, or more recently a meta-functional of the Minnesota M06 family. Changing the functional can yield changes of the gas-phase ionization potential up to an eV. Unfortunately, we cannot compare these DFT values to the most reliable... 

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