Gas-phase thorium clusters from laser ablation suggest magicity of Th\(_{13}^+\)

Laser ablation of a metallic thorium foil produces cationic thorium clusters Th\(_n^+\) composed of up to \(n=15\) atoms as well as oxide clusters Th\(_n\)O\(_m^+\). Mass spectra are recorded using a multi-reflection time-of-flight analyzer. Up to \(n\lesssim 8\), the most abundant species for a given cluster size is the Th\(_n\)O\(_{2n-1}^+\) configuration. Notably, pure thorium clusters Th\(_n^+\) become dominant for \(n > rsim 9\). Production drops sharply after Th\(_{13}^+\) indicating increased relative stability associated with a “magic number” cluster size.