Electronic structure of metal–rare gas dimers with sp configuration: Application to strong spin–orbit interaction in HgAr

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In order to describe the electronic states of metal (M)–rare gas (Rg) van der Waals dimers having an sp configuration with a strong spin–orbit interaction, we derived an e/f parity adapted molecular Hamiltonian matrix by adopting a symmetry-adapted atomic orbital approach. The molecular Hamiltonian was constructed by introducing (i) the interaction between the p electron and the attached rare gas atom, VRg, (ii) the exchange interaction between the s and p orbitals, e2/rsp, and (iii) the spin–orbit interaction for the p electron. As a basis set, twelve molecular electronic wave functions were derived by taking into account their e/f parities. We applied the derived molecular Hamiltonian matrix to the first excited 6s6p configuration of HgAr by performing a least-squares fit to the spectroscopically determined term values for the v=0 levels of the a 3Π0−, A 3Π0+, B 3Π1, b 3Π2, and C 1Π1 states. From the results of the least-squares fit, we clarified how the above interactions (i)–(iii) split twelve degenerate molecular wave functions into the eight electronic eigenstates; i.e., a 3Π0−, A 3Π0+, B 3Π1, b 3Π2, c 3Σ+1, d 3Σ0−+, C 1Π1, and D 1Σ+0. On the basis of (i) a critical comparison between the atomic Hamiltonian matrix for Hg and the determined molecular Hamiltonian matrix and (ii) an examination of the mixing among the symmetry-adapted molecular wave functions, characteristic features of the electronic structure arising from the formation of a van der Waals bond, were extracted.