A post-HF study on the interaction of iodine with small polyaromatic hydrocarbons

In this work, we present a theoretical study of the interaction between a diatomic iodine molecule with planar naphthalene and several other small polyaromatic hydrocarbons (PAHs). Our aim was to understand the general characteristics of the potential energy surface (PES) of this system; that is locating various local minima, finding the variation of PES around these optimum points by means of first principle calculations at MP2, SCS-MP2 and CCSD(T) levels of theory. Two basic orientations of the iodine molecule, i.e., parallel or perpendicular with respect to the naphthalene plane, are discussed. The PES of the former was investigated in detail, including the translation and rotation of I-2 (as a rigid rotor) along the naphtalene surface. It was concluded that, although the perpendicular conformations are usually 1 kcal mol(-1) more stable than the parallel conformation, this small difference does not exclude the presence of both conformations in the gas phase. Both structures were stable enough to hold more than 20 vibrational states. NBO analysis showed that the mutual polarization effects were greater for the perpendicular conformation. It was also observed that the I-2+naphtalene dimer interaction is almost twice of that of I-2+naphtalene, showing the long range character of the interaction.