Si(3P) + OH(X2Pi) interaction: long-range multipolar potentials of the eighteen spin-orbit states.

Eighteen spin-orbit states are generated from the open-shell open-shell Si((3)P) + OH(X(2)Pi) interacting system. We present here the behavior of the associated long-range intermolecular potentials, following a multipolar expansion of the Coulombic interaction treated up to second order of the perturbation theory, giving rise to a series of terms varying in R(-n). In the present work, we have considered the electrostatic dipole-quadrupole (n = 4) and quadrupole-quadrupole (n = 5) interactions, as well as the dipole-induced dipole-induced dispersion (n = 6) and dipole-dipole-induced induction (n = 6) contributions. The diatomic OH is kept fixed at its ground state-averaged distance, (r)(v=0) = 1.865 bohr, so that the long-range potentials are two-dimensional potential energy surfaces (PESs) that depend on the intermolecular distance R and on the bending angle gamma = angleSiGH, where G represents the mass center of OH. From the calculated properties of the monomers, such as the dipole and quadrupole moments and static and dynamic polarizabilities, we have determined and tabulated the long-range coefficients of the multipolar expansion of the potentials for each matrix elements. The isolated monomer spin-orbit splittings have been included in the final matrix, whose diagonalization gives rise to 18 adiabatic potentials. Then, the adiabatic states have been compared to potential energies given by supermolecular ab initio calculations resulting in a general good overall agreement.