Field-dressed potential energy curves for Hj

As in atoms, relativistic terms due to the interaction between the spin and orbital angular momenta of nuclei and electrons of the molecule must be added to the electronic Hamiltonian. There is also a magnetic interaction energy created by the orbital motion of the electrons and the rotational motion of the electrically charged nuclei. The relativistic effects consist mainly of three parts  

Interaction between the spin and orbital angular momenta of the electrons, 

Interaction between the electron spin and the rotational angular momenta of the nuclei, HSR = spin-rotation operator. 

Interaction between the spins of different electrons, Hss = spin-spin operator. 

The form of the spin-orbit Hamiltonian has been given by Van Vleck (1951) and is an extension to diatomic molecules of the solution for the relativistic equation originally derived for a two-electron atom  

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Figure 3.12 Field-dressed potential energy curves for HJ interacting with a 532nm laser field. The field-dressed diabatic curves are shown as full lines. The field-dressed adiabatic curves, shown as dotted and dashed curves, correspond respectively to laser intensities of 1 x 1013 W/cm2 and 4 x 1013 W/cm2 (from Giusti-Suzor, et al., 1995).

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