An ab initio CCSD(T) potential energy surface for the Ar–I2(X) complex

The van der Waals interaction of Ar atom with I2 molecule is studied using the coupled-cluster with single and double excitations and a noniterative perturbation treatment of triple excitations (CCSD(T)) method. Augmented correlation consistent basis sets, aug-cc-pVQZ, are used for Ar atom, supplemented with an additional set (3s 3p 2d 2f 1g) of bond functions. Effective-core potentials (ECPs) augmented with diffusion (sp) and polarization (3df) functions, (SDD+G(3df)), have been employed for the halogen I atoms. The potential energy surface of the ground electronic state of Ar–I2 show a double-minimum topology with an isomerization barrier of 132 cm−1; this is rather high, indicating the existence of two stable isomers at low temperatures. We calculated the J=0 vibrational vdW levels and the lowest two n=0,1 assigned to linear isomers, while the n=2 level is found only 1.7 cm−1 above the n=1 and corresponds to the T-shaped configuration. The CCSD(T) dissociation energies for the linear and T-shaped configurations are found to be D0L=237.8 cm−1 and D0T=212.0 cm−1, confirming previous theoretical and experimental investigations.