Investigation of vibrational states of the ArHCl+ cation in the electronic ground state

The potential energy surface (PES) of the electronic ground state of the ArHCl+ molecular ion is calculated by the multireference single- and double-excitation configuration interaction (MRD-CI) technique. An analytical representation of the potential energy data is obtained in the form of a power series. The vibrational eigenvalue problem is treated with high accuracy on the basis of the variational method using a direct product basis contracted in two steps (truncation/recoupling method). Unexpectedly for such a weakly bound system the spectrum turns out to be of a rather regular nature up to the first dissociation energy, allowing for an assignment of quantum numbers to a major part of the vibrational states. Furthermore, the wave functions are analysed together with several geometrical and energetic characteristics of the various vibrational states. (C) 1999 Elsevier Science B.V. All rights reserved.