Metastable inner-shell molecular state

Metastable innershell molecular state (MIMS) for quasimolecules in atomic collisions at high impact velocity, Winterberg predicted the existence of inner-shell-bound metastable keV molecules under high pressure and their use for the ignition of thermonuclear reactions. Metastable Innershell Molecular State (MIMS) that is homologous to the rare-gas excimers was proposed by Bae in 2008 For more details, refer to the last section of this article, "Other models for inner-shell-bound molecules."
To search for many-body effects in the highly compressed stellar materials, Bae and his colleagues at BNL generated and studied such materials by impacting various bio and water nanoparticles at hypervelocities (v~100 km/s) on various targets. In the analysis of the BNL signals, Bae discovered the BNL results with buckyball ions (C60 ) impacting on an Al target in an independent tabletop apparatus that is orders of magnitude more compact than that at BNL. The result also demonstrated the potential of scaling up of X-ray generation with nanoparticle impact by exploiting C60 ions, of which currents can be readily scaled up to an industrial quantity in a tabletop apparatus. Bae also proposed a more elaborated MIMS model that is homologous to rare gas excimer molecules was developed and predicted that all elements in periodic table are subjected to the MIMS formation. In his papers, The predicted bond lengths of the bismuth and uranium K-MIMS are in excellent agreement with that estimated from the experimental results by researchers at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany
MIMS model
In typical environment, the ground state of rare gas atom dimers is electronically non-binding, but if their closed outershell electrons are excited, dimers can readily form transient bound molecules, excimers. For example, the ground He2 state (1sσg 1sσu : X Σg ) is electronically repulsive, but excitation of an electron can lead to Rydberg states (for example, the metastable, 1sσg 1sσu2sσg: a Σu ) with the He2 core. The low-lying metastable excited states of the dimer (the He2 excimer) are strongly covalently bound. The metastable excimer can radiate to the free repulsive ground state.
The excimer formation is a critical step in energy-efficient conversion of the atomic electron excitation/ionization energy into the radiation energy in rare gas plasma for the excimer lasers. Without forming the excimers, the energy of the excited atoms would be rapidly lost by non-radiative collisional decay processes in the high pressure environment. In other words, the excimer formation is a crucial step needed for efficient transformation of the atomic excitation energy to the radiation energy in an ultra-high pressure environment. Analogously, the MIMS formation is a crucial step required for efficiently transforming the atomic core-excitation energy into the radiation energy. The statistically distributed K-MIMS decays into the lower L-shell MIMS (L-MIMS), ,
by emitting an X-ray photon, and subsequently the L-MIMS dissociates into two atomic ions. Currently, such heteronucleus MIMS formed with H and He with other elements are proposed to be observed in H and He impact on a range of solids. Based on Equation of States (EOS) of materials, The quasimolecule can be considered as a collisional complex that is a manifestation of MIMS during collision processes. However, the actual experimental searches for such X-ray signatures of the quasimolecule in X-ray generation in heavy ion impact started much later, in the 1970s. The carbon Kα X-ray generation cross sections for the heavy ions, such as Ar and Xe , were discovered to be several orders of magnitude larger than those by light ions, such as H and He , which were consistent with the values predicted by the direct Coulomb scattering theory. In his papers, Bae proposed that the production of the shocked regions that are able to bear abundant MIMS by the heavy ion impacts as in the nanoparticle impact demonstrated the possibility of forming transient molecular states with closed-shell electrons in ab initio calculations for the first time for frozen or slow moving ion systems that can be approximated with the Born-Oppenheimer approximation.

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