Methods for calculating the bound state energies of van der Waals trimers: Applications to Ar3

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Abstract
Several different methods for calculating the energy levels of van der Waals trimers are compared for the case of Ar3. These include solution of the coupled equations in a basis set of hyperspherical harmonics and various three‐dimensional basis set expansions. It is found that a basis set expansion in Jacobi coordinates gives results that are adequate for calculating the energy levels of the lowest few vibrational states, and that this method is computationally cheap enough to be extended to handle atom–atom–diatom complexes. The transition dipole moments for the lowest allowed transitions of Ar3 are estimated, and found to be about 7×10−5 D. The effects of three‐body forces on the energy levels are investigated, and found to be large enough to determine from high‐resolution spectroscopic experiments.