Theoretical study on the structure and the frequency of isomers of the naphthalene dimer

Saeki, Morihisa; Akagi, Hiroshi; Fujii, Masaaki*

The structures of the naphthalene monomer and dimer were investigated by performing vibrational analysis. The optimized geometry of the naphthalene monomer was found to be distorted out of plane in MP2/6-31G, MP2/6-31G*, MP2/6-31+G*, MP2/6-311G calculations, while it maintains the plane of symmetry in MP2/6-31G*(0.25) and MP2/cc-pVDZ. Based on the result of the geometrical optimization in the monomer, the MP2/cc-pVDZ level was employed in a calculation of the dimer. The naphthalene dimer has four stable isomers: the naphthalene molecules are bound by the - interaction in three isomers and by the C-H... interaction in one isomer. The relative stability of the isomers suggested an enhancement of the - interaction in the structures with lower symmetry, which could be explained using a molecular-orbital model. Based on the calculated frequencies and the infrared spectrum, the vibrational modes available to experimentally distinguish the isomers were predicted.