Theoretical potential energy surfaces for excited mercury trimers

Potential energy surfaces are calculated for electronic excited states of mercury trimers (Hg3) correlating to Hg(61P,63P) + Hg(61S) + Hg(61S) asymptotes. The theory is based on the diatomics-in-molecules (DIM) method with the aid of the existing ab initio diatomic potential energy curves and the atomic spin-orbit interaction parameters. Stability of the trimers with C2v symmetry is investigated in detail. It is thus shown that the lowest excited level corresponds to the metastable A1′ state in the equilateral triangle (D3h) configuration, which is located at 3.04 eV above the energy of infinitely separated ground-state atoms. The energy of dipole allowed transition from the bottom of the A0u+ state to the ground X0g+ state in the symmetric linear (D∞h) configuration is predicted to be 2.55 eV (4870 Å), which accounts for the well known 4850 Å continuum emission observed through many previous experiments. The origin of the 2170 Å fluorescence band is discussed in connection with higher excited states of Hg3.