Ab initio potential energy surface for Ar 3 +

The potential energy surface (PES) of linear Ar ₃ ⁺ is calculated at the MP4/6-31G* level including all single, double, triple and quadruple excitations. The results show that the PES of the linear Ar ₃ ⁺ has a very flat valley along the asymmetric stretching vibration normal mode, ν₃. A higher level quadratic configuration interaction calculation including single, double and triple substitutions QCISD (T) along this flat valley suggests that an asymmetric geometry energy minimum reported earlier based on MP2 1] is due to symmetry breaking in UHF. The global minimum of the PES is found to be for the symmetric geometry atR _ab =R _bc =2.66±0.01 Å, which is in good agreement with the MRD-CI calculation 2] and expectations from our earlier photodissociation experiments 3]. The calculational results are compared with other theoretical calculations, and are discussed in the context of the photodissociation and dynamics of dissociation experiments conducted on Ar ₃ ⁺ .