Recent progress in experimental and computational methods for the study of negative atomic ions has greatly improved the knowledge about the structural and dynamic properties of the negative alkaline-earth ions. This review deals in particular with the stable ground states in , , and and with the metastable quartet states ( , , and ) observed in , , , and . Future perspectives are discussed.
Apropos to the growing interest in the study of long-range interactions which for their applications in cold atom physics, we have performed theoretical calculation for the two-dipole
C6 and three-dipole
C9 dispersion coefficients involving alkaline-earth atoms with alkaline-earth atoms and alkaline-earth ions. The
C6 and
C9 coefficients are expressed in terms of the dynamic dipole polarizabilities, which are calculated using relativistic methods. Thereafter, the calculated
C6 coefficients for the considered alkaline-earth atoms among themselves are compared with the previously reported values. Due to unavailability of any other earlier theoretical or experimental results, for the
C6 coefficients for alkaline-earth atoms with alkaline-earth ions and the
C9 coefficients, we have performed separate fitting calculations and compared. Our calculations match in an excellent manner with the fitting calculations. We have also reported the oscillator strengths for the leading transitions and static dipole polarizabilities for the ground states of the alkaline-earth ions, i.e., Mg
+, Ca
+, Sr
+, and Ba
+ as well as the alkaline-earth atoms, i.e., Mg, Ca, Sr, and Ba. These, when compared with the available experimental results, show good agreement.
Alkaline-earth dimers are now been used, as new grounds for, testing fundamental physics laws, precision measurements and quantum computation. As a starting point for such experiments, one needs a very good knowledge of the electronic structure, energetics and long-range behavior of these molecular ions. We perform accurate ab initio calculations for the ground and low-lying excited states of Be2+, Mg2+, Ca2+ and Sr2+ molecular ions. We have also calculated the spectroscopic constants, electronic transition dipole moments, polarizabilities and long-range dispersion coefficients for the various alkaline-earth ionic dimers. We have extended our calculations to study heteronuclear species of alkaline-earth molecular ions, like BeCa+, and also mixed alkali alkaline-earth species like NaCa+. We calculated photoassociation (PA) pathways for formation of cold molecular ions and also studied corrections to the Born-Oppenheimer Hamiltonian: non-adiabatic couplings and hyperfine structure due to nuclear spins and electric quadrupoles. We believe, this work would lay foundation, not only for new experiments in ultracold physics and chemistry, but would also provide valuable starting point for theoretical calculations involving low temperature scattering and resonant charge transfer.
Most atomic species—roughly 80% of the periodic table—can form stable negative ions in their gaseous phase. The most notable and easily understood exceptions are the noble gas atoms, the symmetry of whose completely filled electron shells offers no handhold for a would-be extra tenant. The alkaline earths—calcium, strontium, barium and their group IIA cousins—are similarly inhospitable, or so the standard textbooks assure us. Two back-to-back reports in a recent issue of Physical Review Letters have now disabused us of this venerable assurance.
Strontium, barium and radium are predicted to have stable negative ions of ns2np designation, on the basis of eigenchannel R-matrix calculations performed in LS coupling for the negative ion of each alkaline-earth atom. The calculations also confirm earlier studies indicating that the negative ion of calcium is stable and that corresponding 2P degrees states in beryllium and magnesium are unstable shape resonances. The much larger polarisability of the heavier alkaline earths play a crucial role in binding the additional electron. The analysis uses quantum defect theory in its generalised form appropriate for long-range motion in a dipole polarisation potential.
Accurate knowledge of interaction potentials among the alkali-metal atoms and alkaline-earth ions is very useful in the studies of cold atom physics. Here we carry out theoretical studies of the long-range interactions among the Li, Na, K, and Rb alkali-metal atoms with the
Ca+,
Ba+,
Sr+, and
Ra+ alkaline-earth ions systematically, which are largely motivated by their importance in a number of applications. These interactions are expressed as a power series in the inverse of the internuclear separation
R. Both the dispersion and induction components of these interactions are determined accurately from the algebraic coefficients corresponding to each power combination in the series. Ultimately, these coefficients are expressed in terms of the electric multipole polarizabilities of the above-mentioned systems, which are calculated using the matrix elements obtained from a relativistic coupled-cluster method and core contributions to these quantities from the random-phase approximation. We also compare our estimated polarizabilities with the other available theoretical and experimental results to verify accuracies in our calculations. In addition, we also evaluate the lifetimes of the first two low-lying states of the ions using the above matrix elements. Graphical representations of the dispersion coefficients versus
R are given among all the alkaline ions with Rb.
Apropos of the growing interest in the study of long-range interactions for their applications in cold-atom physics, we perform theoretical calculations for the two-dipole
C6 and three-dipole
C9 dispersion coefficients involving alkaline-earth-metal atoms with alkaline-earth-metal atoms and alkaline-earth-metal ions. The
C6 and
C9 coefficients are expressed in terms of the dynamic dipole polarizabilities, which are calculated using relativistic methods. Thereafter, the calculated
C6 coefficients for the considered alkaline-earth-metal atoms are compared with previously reported values. Due to unavailability of any other earlier theoretical or experimental results, for the
C6 coefficients for alkaline-earth-metal atoms with alkaline-earth-metal ions and the
C9 coefficients we perform separate fitting calculations and compare the results. Our calculations match in an excellent manner with the fitting calculations. We also report the oscillator strengths for the leading transitions and static dipole polarizabilities for the ground states of the alkaline-earth-metal ions, i.e.,
Be+,Mg+,Ca+,Sr+, and
Ba+, as well as the alkaline-earth-metal atoms, i.e., Be, Mg, Ca, Sr, and Ba. These show good agreement when compared with the available experimental results.