Structure of the chlorobenzene–argon dimer: Microwave spectrum and ab initio analysis

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Abstract
The rotational spectra of the Cl35 and Cl37 isotopes of the chlorobenzene–argon van der Waals dimer have been assigned using Fourier transform microwave spectroscopy techniques. Rotational constants and chlorine nuclear quadrupole coupling constants were determined which confirm that the complex has Cs symmetry. The argon is over the aromatic ring, shifted from a position above the geometrical ring center towards the substituted carbon atom, and at a distance of about 3.68 Å from it. This distance is 0.1–0.2 Å shorter than the similar distance in the benzene–argon and fluorobenzene–argon complexes. Experimental results are confirmed and explained with the help of second-order Mo/ller–Plesset perturbation calculations using a VDZP+diff basis set. The complex binding energy of the chlorobenzene–argon complex is 1.28 kcal/mol (fluorobenzene–argon, 1.17; benzene–argon, 1.12 kcal/mol) reflecting an increase in stability caused by larger dispersion interactions when replacing one benzene H atom by F or by Cl. The structure and stability of Ar⋅C6H5–X complexes are explained in terms of a balance between stabilizing dispersion and destabilizing exchange repulsion interactions between the monomers.