Experiments with cold ion–atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk+ (Alk = Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotentials, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium–alkali-metal-atom molecular ions in modern experiments with cold ion–atom mixtures.

In this theoretical work, we calculate potential energy curves, spectroscopic parameters and transition dipole moments of molecular ions BeX + (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarization potentials, and full configuration interaction (CI). We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion-atom colliding systems by stimulated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion-atom cold collisions and experimental realization of cold molecular ion formation.

The BeCs+ system represents a possible future candidate for the realization of samples of cold or ultra-cold molecular ion species that it has been not yet investigated experimentally nor theoretically....

Based on the ab-initio approach and using the non-empirical pseudo-potential formalism for Be2+, Na+, K+ and Rb+ cores, large Gaussian basis sets and full valence configuration interaction (FCI), alkali-metal atom and the Beryllium ionic pairs are treated as effective two-electron systems. The potential energy curves and their spectroscopic constants for the low-lying excited states of different1,3Σ+, 1,3Πand 1,3Δ symmetries of these molecular ions have been performed. In addition to the vibrational properties, permanent and transition dipole moments functions have been also calculated and analyzed. The lifetimes of the vibrational states of the ground state are calculated taking into account the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission induced by black body radiation. The radiative lifetimes of the vibrational levels of the first A1Σ+ and second C1Σ+excited states are calculated using both ‘Franck-Condon’ and ‘Sum rule’ approximations. In all studied alkali-metal Beryllium molecular ions the ground states X1∑+ have much longer lifetimes than any excited states with an order of second, while an order of nanosecond is found for the first and second excited states, A1Σ+ and C1Σ+.

Ab initio calculations of alkaline diatomic molecule interactions with alkaline atoms provide detailed information about their electronic structure, vibrational frequencies, and spectroscopic properties, which are difficult to measure experimentally. This knowledge can aid in designing and interpreting experiments and guide the development of computational models and advanced dynamical calculation. Using the quantum chemistry ab initio methods based on multi-reference configuration interaction with Davidson correction (MCSCF/MRCI + Q), atomic effective core potentials, core-polarization potentials, and the interactions between the sodium atom and the NaRb diatomic molecule are investigated. To describe the potential energy surfaces of the RbNa2 system, we introduce two geometries described in the Z-matrix coordinates (R e, R, θ). Potential energy surfaces of the ground state 12A′ and the first excited state 22A′ were calculated for different approach directions of the sodium atom to the NaRb molecule and two geometries were considered. The first geometry is where the Na atom approaches the Rb atom of the RbNa dimer, and the second one is when it approaches the Na atom of the RbNa dimer. Global minima of the ground and first excited states and conical intersections between these states are determined for both geometries. The RbNa dimer in interaction with the sodium atom is found to be strongly attractive in its first excited state, which may be important for the experimenters particularly in the field of cold alkali polar dimers. Thereafter, the potential energy curves correlated to the lowest-lying dissociation limits are calculated in the linear form for the two geometrical cases (angle θ at 180°) and the atomic arrangement effect is observed.

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The electronic structure of BeSe and BeTe molecules has been investigated using the ab initio CASSCF/(MRCI + Q) method at the spin-free and spin-orbit level. The potential energy curves, the permanent dipole moment, the spectroscopic constants T e, R e, ωe, and B e, and the dissociation energy D e are determined in addition to the vertical transition energy Tv. The molecules’ percentages of ionic character are deduced, and the trends of the spectroscopic constants of the two molecules are compared and justified. A ro-vibrational study is performed using the canonical function approach to calculate the constants E v, B v, and D v and the turning points R min and R max. All the ground-state vibrational levels have also been investigated. The radiative lifetimes of vibrational transitions among the electronic ground states are also discussed. The results for BeSe have been compared with the previously published data while those for BeTe molecules are presented here for the first time.