Model Calculations of Potential Surfaces of van der Waals Complexes Containing Large Aromatic Molecules

Mary Jo Ondrechen, Joshua Jortner, Ziva Berkovitch-Yellin

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In this paper we report the results of model calculations of the nuclear potential surfaces of van der Waals complexes consisting of large aromatic molecules and rare-gas (R) atoms. These potentials were constructed as a superposition of pairwise atom-atom potentials, the R-carbon atom pair potentials being taken from heats of adsorption of rare-gas atoms on graphite, while the R-hydrogen atom pair potentials are estimated by using empirical combination rules. The binding energies of the tetracene (T) complexes TR, are 0.7 kcal mol−1 for Ne, 1.5 kcal mol−1 for Ar, 1.8 kcal mol−1 for Kr, and 2.2 kcal mol−1 for Xe, while the equilibrium distance between R and the molecular plane of tetracene is 3.0 Å for Ne, 3.45 Å for Ar, 3.5 Å for Kr, and 3.7 Å for Xe. Low-frequency, large-amplitude motion of the R atoms parallel to the molecular plane along the long molecular axis is predicted for TR, and TR2 complexes. The potential for TR, along the long molecular axis has a symmetric double-well form, giving rise to a “tunneling-type” motion of the R atom. For the TR2 complexes, the configuration with two R atoms located on the same side of the aromatic molecule is energetically favored over that with the two R atoms on opposite sides. No chemical isomers are expected to exist for the TR, and TR2 complexes, while for TRn complexes with n ≥ 3 the possibility of the existence of two or more nearly isoenergetic isomers is indicated. The applications and implications of these data for the elucidation of some features of excited-state energetics and dynamics of such van der Waals complexes are considered.

Original languageEnglish
Pages (from-to)6586-6592
Number of pages7
JournalJournal of the American Chemical Society
Issue number22
StatePublished - Nov 1981


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