A model for the rovibrational energy levels of a complex formed between a rare gas atom and a spherical top molecule is developed, specifically for a tetrahedral XY(4) molecule in its ground and its triply degenerate vibrational states. Under the assumption that the tetrahedral molecule remains undistorted upon complexation, a large amount of the tetrahedral symmetry is retained in the complex. Using symmetry adapted terms to represent the anisotropy of the intermolecular potential, the perturbations to the energy levels of the tetrahedral molecule caused by the intermolecular potential have been considered. Correlation diagrams showing the pattern of these internal rotor states between the free rotor and rigid molecule limits have been constructed.