Ab initio quasirelativistic calculations on angular momentum and magnetic couplings of molecular electronic states

We formulate an ab initio method of quasirelativistic calculations on angular momentum and magnetic transition matrix elements between adiabatic electronic states of molecules. Our approach is based on the construction of a state-selective effective Hamiltonian and transition density matrices by means of the multireference many-body perturbation theory. Pilot applications to the evaluation of B0_u⁺→ B 1_u predissociation matrix elements in I₂ and interactions in the B0⁺_u ∼ B1_u complex of Te₂ are reported.