Does a neutral dimercury molecule exist?
There has been recent research on mercury dimers in its ground state. Bond energies, transition energies, band spectrum and other spectroscopic parameters has been calculated. Here are the abstracts of two papers on mercury dimer:



  The potential energy curve of the ground electronic state of the $\ce{Hg}$ dimer has been calculated using the CCSD(T) procedure and relativistic effective core potentials. The calculated binding energy ($\pu{0.047 eV}$) and equilibrium separation ($\pu{3.72 Å}$) are in excellent agreement with experiment. A variety of properties, including the second virial coefficient, rotational and vibrational spectroscopic constants, and vibrational energy levels, have been calculated using this interatomic potential and agreement with experiment is good overall.(Source)


  The mercury dimer is among the most weakly bound metal dimers and has been extensively studied. The ground state $\ce{O^+_g}$ dissociation energy has been considered to lie between $\pu{0.55 eV}$ ($\pu{440 cm−1}$) and $\pu{0.091 eV}$ ($\pu{730 cm−1}$). We report here a spectroscopic study of $\ce{Hg2}$ in a supersonic jet. The first optical transition, $\ce{1_u←O^+_g}$, was characterized by its fluorescence excitation spectrum and the binding energy of the ground state has been measured precisely through the threshold of collision induced dissociation of $\ce{Hg2 1_u}$ to $\ce{Hg(^1S_0)+Hg(^3P_0)}$.(Source)