An electrostatic model for the energetics of large heterocluster cations

In this paper we extend and apply the electrostatic model [Jortner, J.; Even, U.; Leutwyler, S.; Berkowitch-Yellin, Z. J. Chem. Phys. 1983, 78, 305] for the calculation of the ionization potentials of M·A_n heteroclusters (M = benzene, anthracene (ANT) and 9,10-dichloroanthracene (DCA); A = Ar and Kr). The electrostatic contributions to the ionization potential shift δΙ of the heterocluster relative to the bare molecule (consisting of charge-induced dipole and induced dipole-induced dipole M⁺-A_n and M-A_n interactions) were evaluated using the entire π and σ atomic charge densities of M⁺ and of M. Molecular wave functions for ANT, for DCA, and for their cations were computed using the semiempirical MNDO method and utilized for the computation of the atomic charges by the Mulliken and the Löwdin methods. The Löwdin charges provide the best description of δΙ. The modification of the calculated δΙ for benzene·Ar by the improvement of the molecular wave functions for benzene⁺ and benzene was also explored. The electrostatic model, together with structural data, accounts for the experimental δΙ data of benzene·Ar₁, ANT·Ar₁, ANT·Kr₁, DCA·Ar₁, and DCA·Kr₁. The electrostatic model in conjunction with finite temperature molecular dynamics simulations accounts well for the size dependence of δΙ for DCA·Ar_n and DCA·Kr_n (n = 1-18) heteroclusters.