Three attempts and one success in addressing the bandgap closure in mercury clusters

We review the ups and downs of three projects, in which we tried to address the problem of bandgap closure in mercury clusters over the last 18 years. The first project aimed at measuring the polarizability of neutral mercury clusters. This project stopped with the appearance of the polarizability measurements from Knighfs group. In the second project we measured the photoelectron spectra of mass-selected negatively charged mercury clusters Hg-_n in the size range n = 3-250. The spectra were characterized by gaps which shrink with increasing n Those gaps represent the s-p excitation bandgaps of the corresponding neutral clusters. Extrapolation of the bandgap to higher cluster size indicated complete closure at the size range n = 400 ± 30, a considerably larger value than previously reported (n = 80-100). We present here new photoelectron spectra taken with 6.4 eV photons which reinforce the above conclusion. In the third project we measured the photoelectron spectra of Hg_nI- clusters. We had hoped to extract from these spectra the static dielectric response of neutral mercury clusters. We present these recent results and explain their failure to deliver the desired dielectric response.