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Ab initio effective spin-orbit operators (AESOP), derived from relativistic effective potentials based on Dirac-Fock atomic wavefunctions, have been used to calculate the spin-orbit coupling in the ground $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi i$ state of OH as a function of internuclear distance. Spin-orbit interactions between the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi j$ state and the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma -$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ states arising from the $O(3P)+H(2S)$ asymptote have been taken into account as well as interaction with the $A2\Sigma +$ state which correlates with the $O(1D)+H(2S)$ asymptote. The ground-state was represented by an 11 configuration MCSCF wavefunction while the excited states were determined by full valence first-order CI calculations using the ground state molecular orbitals. Results near $Rc$ are in excellent agreement with experimentally determined spin-orbit splittings. Spin recoupling is found to play an important role in the variation of the spin-orbit splitting with R. The coupling constant, A, does not decrease monotonically to the oxygen value as previously though. Vibrational averaging of our calculated values gives excellent agreement with the experimentally determined values of Coxon and Foster [Caon. J. Phys., to be published] through $\upsilon =10$.