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Register a new userTunnel ionization of open-shell atoms
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A generalized ADK (Ammosov-Delone-Krainov) theory for ionization of open shell atoms is compared to ionization experiments performed on the transition metal atoms V, Ni, Pd, Ta, and Nb. Our theory is found to be in good agreement for V, Ni, Pd, and Ta, whereas conventional ADK theory overestimates ionization by orders of magnitude. The key to understanding the observed ionization reduction is the angular momentum barrier. Our analysis shows that the determination of the angular momentum barrier in open shell atoms is nontrivial. The Stark shift is identified as the second dominant effect responsible for ionization suppression. Finally, these two effects cannot explain the Nb data. An analysis of the electron spins suggests that Pauli blocking might be responsible for the suppression of tunneling in Nb.
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Target ionization processes of alkali atoms by Positronium impact are investigated. Calculations are performed in the frame work of model potential formalism using the Coulomb distorted eikonal approximation. Interesting qualitative features are noted both in the scattered Ps and the ejected electron distributions in differential as well as double differential levels of the collision cross sections.
We have studied an ionization of alkali-metal Rydberg atoms by blackbody radiation (BBR). The results of the theoretical calculations of ionization rates of Li, Na, K, Rb and Cs Rydberg atoms are presented. Calculations have been performed for nS, nP and nD states which are commonly used in a variety of experiments, at principal quantum numbers n=8-65 and at the three ambient temperatures of 77, 300 and 600 K. A peculiarity of our calculations is that we take into account the contributions of BBR-induced redistribution of population between Rydberg states prior to photoionization and field ionization by extraction electric field pulses. The obtained results show that these phenomena affect both the magnitude of measured ionization rates and shapes of their dependences on n. A Cooper minimum for BBR-induced transitions between bound Rydberg states of Li has been found. The calculated ionization rates are compared with our earlier measurements of BBR-induced ionization rates of Na nS and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states except nS with n>15 is observed. Useful analytical formulas for quick estimation of BBR ionization rates of Rydberg atoms are presented. Application of BBR-induced ionization signal to measurements of collisional ionization rates is demonstrated.
The L-subshell ionization mechanism is studied in an ultra-thin osmium target bombarded by 4-6 MeV/u fluorine ions. Multiple ionization effects in the collisions are considered through the change of fluorescence and Coster-Kronig yields while determining L-subshell ionization cross sections from L-line x-ray production cross sections. The L-subshell ionization, as well as L-shell x-ray production cross sections so obtained, are compared with various theoretical approximations. The Coulomb direct ionization contributions is studied by (i) the relativistic semi-classical approximations (RSCA), (ii) the shellwise local plasma approximation (SLPA), and (iii) the ECUSAR theory, along with the inclusion of the vacancy sharing among the subshells by the coupled-states model (CSM) and the electron capture (EC) by a standard formalism. We find that the ECUSAR-CSM-EC describes the measured excitation function curves the best. However, the theoretical calculations are still about a factor of two smaller than the measured values. Such differences are resolved by re-evaluating the fluorescence and the Coster-Kronig yields. This work demonstrates that, in the present energy range, the heavy-ion induced inner-shell ionization of heavy atoms can be understood by combining the basic mechanisms of the direct Coulomb ionization, the electron capture, the multiple ionization, and the vacancy sharing among subshells, together with optimized atomic parameters.
We report on observations and modeling of interspecies magnetic Feshbach resonances in dilute ultracold mixtures of open-shell alkali-metal $^6$Li and closed-shell $^{173}$Yb atoms with temperatures just above quantum degeneracy for both fermionic species. Resonances are located by detecting magnetic-field-dependent atom loss due to three-body recombination. We resolve closely-located resonances that originate from a weak separation-dependent hyperfine coupling between the electronic spin of $^6$Li and the nuclear spin of $^{173}$Yb, and confirm their magnetic field spacing by ab initio electronic-structure calculations. Through quantitative comparisons of theoretical atom-loss profiles and experimental data at various temperatures between 1 $mu$K and 20 $mu$K, we show that three-body recombination in fermionic mixtures has a $p$-wave Wigner threshold behavior leading to characteristic asymmetric loss profiles. Such resonances can be applied towards the formation of ultracold doublet ground-state molecules and quantum simulation of superfluid $p$-wave pairing.
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