ABINITIO POTENTIAL-ENERGY SURFACE FOR AR-3(+)

The potential energy surface (PES) of linear Ar3+ 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 Ar3+ has a very flat valley along the asymmetric stretching vibration normal mode, nu3. 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 at R(ab) = R(bc) = 2.66 +/- 0.01 angstrom, 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 Ar3+.