ON THE NATURE OF THE INTERACTION ENERGY IN THE AR-CL2 COMPLEX

An analysis of the potential energy surface of the Ar-Cl2 complex was performed using the perturbation theory of intermolecular forces and s upermolecular MPPT approach. Two types of minimum were found which cor respond to the linear Ar...Cl-Cl structure (a primary minimum, D(e) = 222 cm-1, R(e) = 4.5 angstrom) and to the T-shaped structure with the argon atom perpendicular to the molecular axis (a secondary minimum, D (e) = 207 cm-1, R(e) = 3.8 angstrom). The small difference between the D(e) values does not exceed 16 cm-1 and is mainly due to the inductio n effects which are larger for the linear form. Although the linear fo rm is lower in energy, the T-shaped isomer may be more stable because its zero-point energy is smaller than that of the linear form by about 18 cm-1 (F.-M. Tao and W. Klemperer, J. Chem. Phys., 97 (1992) 440). Indeed, only the T-shaped form is detected in the excitation and micro wave spectroscopy experiments. It is also found that the electron dens ity distribution in the Cl2 case may be visualized as a dumbbell with flattened ends. By comparison, the CIF distribution can be viewed as a n unsymmetrical dumbbell with a dent at the chlorine atom.