Photodetachment studies of extended excited states in $I−Xen$ clusters $(n=1–54)$

We present a comprehensive experimental study of bound excited states in $I−Xen$ clusters $(n=1–54),$ using photoelectron spectroscopy and energy-dependent action spectroscopy. Starting at $n=4,$ the electron detachment action spectra developed peaks lying in energy lower than the vertical binding energy. This behavior has been shown for both final spin states of the neutral iodine. It indicates the existence of bound electronic states extended over the xenon cluster. The peaks lying in energy below the $J=1/2$ detachment continuum of the iodine $(n>4)$ were detected over the whole cluster size range of $I−Xen$ using electron detachment action spectroscopy. For the bound states relating to the $J=3/2$ continuum, in the size range $n=4–12,$ thermionic emission has marked the existence of bound states. For $n>12,$ these states were stabilized and detected via two-photon excitations. The picture, unveiled from the above photoelectron and action spectra, is the gradual evolution of bound excited states on the xenon solvent cluster. The critical size for the binding of an excited electron is $n=4.$ At the largest cluster interrogated, $I−Xe54,$ the binding energy amounts to 170 meV. We compare these states to the ground electronic state of $Xen−$ clusters, and discuss the differences between the experiments and model calculations.