Time-resolved relaxation dynamics of Hg _n ^- (11≤n≤16,n= 18) clusters following intraband excitation at 1.5 eV

Electron-nuclear relaxation dynamics are studied in Hg _n ^- (11≤n≤16,n= 18) using time-resolved photoelectron imaging. The excess electron in the anion uniquely occupies the p band and is excited intraband by 1.53 eV pump photons; the subsequent dynamics are monitored by photodetachment at 3.06 eV and measurement of the photoelectron images as a function of pump-probe delay. The initially excited state decays on a time scale of ∼ 10 ps, and subsequent relaxation dynamics reveal a smooth evolution of the photoelectron spectra towards lower electron kinetic energy over 50-100 ps. Qualitatively, the relaxation process is captured by a simple kinetic model assuming a series of radiationless transitions within a dense manifold of electronic states. All the clusters studied show similar dynamics with the exception of Hg ₁₁ ^-, in which the initially prepared state does not decay as quickly as the others.