Towards comprehending the superatomic state of matter

Photoelectron imaging experiments for the negative ions, Pt− and WC− at a photon energy of 2.33 eV, are highlighted. In the Pt− photoelectron angular distribution (PAD), intense signatures from the electron affinity (EA) transition 3D3 ← 2D5/2, as well as several features from the excited states of Pt−, 2D3/2 and 2S1/2, were observed. Present in the PAD of the valence isoelectronic diatomic molecule WC−, are several transitions originating from the 2Δ3/2 ground and higher energy 2Δ5/2 and 4Σ− excited states. Significantly, the spectroscopic transitions arising from WC− exhibit similarities with those in Pt−, providing insight into the reactivity of WC and Pt surfaces. Discussion regarding the photoelectron spectra of several other isoelectronic diatomic-elemental species further reveals quantitative aspects of the superatom concept. The recent surprising findings in this field are opening a new realm of studies pertaining to the behavior of matter governed by its unified atom/superatomic character.