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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. [Copyright &y& Elsevier]

Techniques of quantum and nonlinear classical mechanics are employed to study the photodissociation dynamics of NeBr2(B) near the Br2 dissociation threshold. A time-dependent treatment is used to obtain the absorption spectrum for the B←X transition. As energy increases up to 3600 cm−1, the spectrum shows a progressive congestion but narrow peaks appear again close to the Br2 dissociation limit. These peaks are associated with long lived resonances that develop nodes along the minimum energy path of the linearization. Periodic orbit (PO) analysis in two dimensions is carried out for the van der Waals NeBr2 system and POs that emerge from saddle-node bifurcations are found to be related to the structure of the above resonances. [Copyright &y& Elsevier]