Effect of Repulsive Electronic States on the Parameters of the Fine Structure of the Ground Electronic State of an OH Radical

Calculations of the contribution from excited electronic states to parameters of the fine structure of the ground electronic state of an OH radical are made in the framework of perturbation theory (Van Vleck contact transformations). The potential energy functions of the electronic states and required matrix elements of spin-orbit and electron-rotation coupling are found from first principles. It is shown that repulsive (unbound) excited electronic states play a crucial role in the dependence of parameters of the fine structure of the ground state on the magnitude of the vibrational excitation.