Vibrational states and structure of Ar3: The role of three-body forces

Abstract

Vibrational energies and eigenfunctions of Ar3, including some pertaining to highly excited states, are computed, and insights into their dynamical and structural properties are obtained. The method used employs the vibrational self-consistent-field (SCF) theory in hyperspherical coordinates as a first approximation. Exact results are obtained by configuration interaction, using the SCF states as an efficient basis. A focal point of the study is the effect of three-body potentials on the vibrational spectrum. Axilrod–Teller and other three-body potentials are used to examine this. It is found that the effect of three-body forces on the spectrum is substantial, and larger than effects due to uncertainties in the presently known two-body Ar–Ar potentials. This suggests that experimental spectroscopy of Ar3 may be used to determine reliable three-body forces among Ar atoms. It is also shown that the three-body double-dipole–quadrupole interaction, while less important than the Axilrod–Teller one, has a significant effect on the vibrational spectrum. Finally, a detailed analysis is made of the Ar–Ar distance distributions in the various states, of the structural distributions of Ar3, and of the properties of the wave functions. We find that the wave functions show well-ordered nodal patterns even for the highly excited large-amplitude states. Thus, these states do not correspond qualitatively to ‘‘liquid-like’’ behavior of the cluster.