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We highlight the spectroscopic and electronic structure of BeCs+ ion, theoretically investigating ground and low lying excited states as well as the cold ion–atom elastic collisions proprieties and laser cooling possibility.

In this theoretical study, we investigate the electronic potential energy curves, spectroscopic parameters, vibrational energy levels and transition dipole moments for the diatomic dications BeRb2+, BeCs2+, and SrRb2+. We consider an ab initio approach based on the use of non-empirical pseudopotentials and parameterized l dependent polarization potentials. Results show that 1-22Σ+ for BeRb2+, 1-52Σ+ for BeCs2+, and 1-32Σ+ for SrRb2+ are repulsive. While the 32Σ+ for BeRb2+, 42Σ+ for BeCs2+, and 42Σ+ for SrRb2+ are metastable states. These states can accommodate some vibrational energy levels. Interesting avoided crossings between some 2Σ+ states are localized and examined. Until now, no experimental and theoretical studies have been made for each system. Consequently, we discuss our results by comparing with some data on similar systems. Besides, the transition dipole moments of the ground state to a few excited states are computed and presented. The information associated with the electronic structures, spectroscopic parameters as well as the transition properties provided in this paper, is anticipated to serve as guidelines for further experimental and theoretical research on diatomic dications considered in this work.

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 Te, Re, ωe, and Be, and the dissociation energy De 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 Ev, Bv, and Dv and the turning points Rmin and Rmax. 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.

An extensive ab-initio quantum chemistry study and a discussion of the possible laser cooling and formation of the heteronuclear ionic MgNa+ molecule is presented in this paper. Our work is based on the use of non–empirical pseudo-potentials for the Mg2+ and Na+ cores, large Gaussian basis sets, parametrized l–dependent polarization potentials, and full valence configuration interaction calculations. We present here adiabatic potential energy curves of the ground and 44 low-lying excited electronic states of 1,3Σ+, 1,3Π, 1,3Δ symmetries, and their spectroscopic parameters (Re, De, Te, ωe, ωexe, and Be). Furthermore, numerous ionic – neutral avoided crossings, specially between higher adjacent electronic states of 1,3Σ+, 1,3Π symmetries, are identified and interpreted. The energy separations between these avoided crossings are also calculated. The electric dipole moment curves have been computed for a wide range of inter-nuclear distances. The vibrational energies are obtained by solving the nuclear Schrodinger equation, using the calculated potential energy curves. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the ground and excited states vibrational level lifetimes. It has been observed that the lifetimes of the ground state vibrational levels are of the order of a second, while those of the excited states, mainly the 21Σ+ state, have the order of a nanosecond.

In this theoretical work, we calculate potential energy curves, spectroscopic pa- rameters 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 stimu- lated 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 potential energy and spectroscopic constants of the ground and many excited states of the Be+He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be2+ core and the electron-He interactions by effective potentials. Furthermore, the core–core interactions are incorporated. This permits the reduction of the number of active electrons of the Be+He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin–orbit interaction. The core–core interaction for Be2+He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be+He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole mome...

International audience; An ab initio approach based on effective core potentials (ECPs), core polarization potentials (CPPs) with three valence electrons and multireference configuration interaction (MRCI) level of calculation is used to determine the adiabatic potential energy curves, the spectroscopic constants and the permanent and transition electric dipole moments of the lowest doublet and quartet electronic states of BaCs. These sates are dissociating into the first six asymptotic limits of the alkali–alkaline earth molecule, BaCs. Only the ground state has been studied in the literature, and the comparison with the available results has shown a very good agreement. The spin–orbit interaction has been included in the next step of our calculation, and its effect on the potential energy curves and spectroscopic parameters on the Ω representation states has been thoroughly studied. Both relativistic and nonrelativistic calculations of permanent and transition dipole moments are also presented, which allows us to determine the influence of relativistic effects on the dipole moment.

The potential energy curves and permanent and transition dipole moments of the neutral SrXe and the ionic Sr+Xe systems are calculated with an ab initio approach using pseudopotential techniques, core polarization potentials, large Gaussian basis sets and full configuration interaction for two electron calculations. The spectroscopic constants of the ground state and lower excited states are in good agreement with the available experimental and theoretical works. The spin–orbit coupling is also included for the ionic system Sr+Xe and the neutral one SrXe. Its effect is significant on the potential energy curves, dipole moments and energy level spacing. For SrXe, the spin–orbit splitting has been considered for the states (2)3Σ0,1, (1,2)3Π0,1,2 and (1)3Δ0,1,2,3.

The structural and electronic properties of the doubly charged diatomic dications BeX2+ (X = Na, K) have been systematically investigated. The ab initio calculations method is based on the use of non-empirical pseudopotentials for the Be2+, Na+, and K+ cores, Gaussian basis sets, and parameterized l-dependent polarization potentials. The potential energy curves and their spectroscopic properties for the low-lying electronic states of 2Σ+, 2Π, and 2Δ symmetries have been determined for the species BeNa2+ and BeK2+ for the first time. Results show, for each diatomic dication, that the ground and the first excited electronic states are repulsive. For both systems, for which no experimental and theoretical data are available, we discuss our results by comparing their potential energies with similar systems. Numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries have been localized and analyzed. Their existence is related to the interaction between the electronic states and to the charge transfer process between the two ionic structures Be(2+)X and Be(+)X(+). Furthermore, the transition dipole functions from the ground state to the 2-102Σ+ and between neighbor electronic states of 2Σ+ symmetry, revealed many abrupt changes, which are localized at particular distances corresponding to the positions of the avoided crossings.

We perform a study on extended adiabatic potential energy curves of nearly 38 states of 1,3$\Sigma^+$, 1,3$\Pi$ and 1,3$\Delta$ symmetries for the (SrNa)$^+$ ion, though only the ground and first two excited states are used for the study of scattering processes. Full Interaction Configuration (CI) calculations are carried out for this molecule using the pseudopotential approach. In this context, it is considered that two active electrons interact with the ionic cores and all single and double excitations were included in the CI calculations. A correction including the core-core electron interactions is also considered. Using the accurate potential energy data, the ground state scattering wave functions and cross sections are obtained for a wide range of energies. We find that, in order to get convergent results for the total scattering cross sections for energies of the order 1 K, one need to take into account at least 87 partial waves. In the low energy limit ( < 1 mK), elastic scattering cross sections exhibit Wigner law threshold law behavior while in the high energy limit the cross sections go as $E^{-1/3}$. A qualitative discussion about the possibility of forming the cold molecular ion by photoassociative spectroscopy is presented., Comment: accepted in EPJ D

The structure and spectroscopic properties of the alkaline hydride BeH2+ ion have been investigated using an ab initio approach based on nonempirical pseudopotentials and parameterized l-dependent polarization potentials. The adiabatic potential energy curves and their spectroscopic constants for the ground and seventeen excited electronic states, dissociating into Be+(2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) + H+ and Be2+ + H(1s and n = 2), of 2Σ+, 2Π, and 2Δ symmetries have been determined. As no experimental data are available, our results are discussed and compared with the few existing theoretical calculations. A very good agreement has been found with the previous theoretical data for the ground state; however many potential energy curves for the higher excited states are presented here, for the first time. Numerous avoided crossings between electronic states for 2Σ+ and 2Π symmetries have been localized and analyzed. Their existence is related to the interaction between the electronic states and to the charge transfer process between the two ionic systems Be2+H and Be+H+. In addition, we have calculated the vibrational energy level spacings of the bound electronic states. Furthermore, the adiabatic transition dipole functions from the X2Σ+ and 22Σ+ states to the higher excited states of 2Σ+ and 2Π symmetries have been evaluated and compared with the available theoretical work. This study represents the necessary initial step towards the investigation of the charge transfer processes in collision between Be+-H+ and Be2+-H.

The electronic structure and the spectroscopic properties for low-lying electronic states of the LiRb+ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb+ and Li+ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non-empirical pseudo potentials for the Li and Rb cores and parametrized l-dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of 2Σ+, 2Π, and 2Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of 2Σ+ and 2Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li+Rb and LiRb+. Moreover, we have determined the transition dipole moments from X2Σ+ and 22Σ+ states to higher excited states of 2Σ+ and 2Π symmetries. For our best knowledge, no experimental data on the LiRb+ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb+ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

In this work, we present the structural and the spectroscopic properties of the alkaline earth BeLi$^{2+}$ ion for all the electronic states dissociating into Be$^{+}$(2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) + Li$^{+}$ and Be$^{2+}$ + Li (2s and 2p). We have used an ab initio approach involving a non-empirical pseudopoential for the Li$^{+}$ and Be$^{2+}$ cores and core-core and core-valence correlation corrections. For our best knoweledge, the adiabatic potential energy curves and the spectroscopic constants for nearly 18 electronic states of $^{2}$Σ $ ^{+}$, $^{2}$Π and $^{2}$ Δ symmetries are determined here for the first time. As neither experimental nor theoretical data are available for BeLi$^{2+}$, our results are discussed and compared with similar systems such as BeH$^{2+}$. Numerous avoided crossings between the electronic states of $^{2}$Σ$ ^{+}$ and $^{2}$Π symmetries have been localised and analysed. Their existences are related to the interaction between the potential energy curves and the charge transfer process between the two ionic systems Be$^{(2+)}$Li and Be$^{+}$Li$^{+}$. Furthermore, we have calculated the adiabatic transition dipole moments from X$^{2}$Σ$ ^{+}$, 2$^{2}$Σ$ ^{+}$ and 3$^{2}$Σ$ ^{+}$ states to the higher electronic states of the same symmetry. This study represents the necessary initial step towards the investigation of the charge transfer processes in collision between Be$^{+}$-Li$^{+}$ and Be$^{2+}$-Li.

The potential energy curves of the electronic states of $^{2}$Σ$^{+}_{g, u}$, $^{2}$Π$ _{g, u}$ and $^{2}$Δ$_{g, u}$ symmetries of the K$_{2}^{+}$ molecular ionic system dissociating into K (4s, 4p, 5s, 3d, 5p, 4d and 6s) + K$^{+}$, have been calculated. The computation was performed using an ab initio approach, where a non-empirical pseudopotential for the K$^{+}$ core has been involved and a core-core and core valence correlation corrections have been added. The spectroscopic constants have been derived and compared with the available theoretical and experimental works. A good agreement has been obtained for the ground and the first excited states. However, a clear disagreement between this study and the model potential work of Magnier and Aubert-Frecon [J. Quant. Spect. Rad. Trans. 78, 2003] has been observed for several excited states. They found that the 5$^{2}$Σ$^{+}_{u}$, 6$^{2}$Σ$^{+}_{g}$, 6$^{2}$Σ$^{+}_{u}$, 7$^{2}$Σ$^{+}_{g}$, 7$^{2}$Σ$^{+}_{u}$, 4$^{2}$Π$_{g}$ and 2$^{2}$Δ$_{u}$ states are repulsive, although they are attractive with potential well depths of 10, 100 and 1000 cm$^{-1}$ in our study. Furthermore, the atomic polarizabilities have been predicted from a vibrational spacing analysis based on the WKB approximation applied on the potential energy at long-range distances. These polarizabilities have been used to reproduce the long range potential interaction for some electronic states.

We study theoretically the structure and spectroscopic properties of the alkali alkaline-earth (LiBe)+ ion. The potential energy curves and their spectroscopic parameters, permanent and transition dipole moments are determined with a quantum chemistry approach. The (LiBe)+ ion is modelled as two valence electron system moving in the field of Be2+ and Li+ cores, which are described by pseudopotentials. In addition, effective core-polarization potentials are included to correct the energy. The molecular calculations are performed using a standard quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarization potentials, and full configuration interaction (CI) calculations. The precision of our spectroscopic parameters are discussed by comparison with currently available theoretical results. A rather good agreement is observed for the ground and first excited states. The permanent dipole moments reveal many abrupt changes, which are localized at particular distances corresponding to the positions of the avoided crossings.

Ab initio calculations are performed for the beryllium hydride ion BeH+ dissociating into Be+(2s, 2p, 3s, 3p and 3d) + H (1s, 2s and 2p) and Be (2s 2, 2s2p, 2s3s, 2p 2, 2s3p and 2s3d) + H+. We have used a standard quantum chemistry approach based on pseudopotential for atomic core representation Be2+, Gaussian basis sets, effective core polarization potentials, and full configuration interaction calculations. Potential energy curves and their spectroscopic constants for the ground state and the first 44 excited electronic states of 1,3Σ+, 1,3 Π and 1,3 Δ symmetries are determined. Their accuracy is discussed by comparing our well depths and equilibrium positions with the previous experimental and theoretical works. A very good agreement with the theoretical calculations and the few available experimental data is observed. Moreover, we localised and analysed numerous avoided crossings between the electronic states of 1,3Σ+ and 1,3 Π symmetries. Their existence are related to the interaction between electronic states and to the charge transfer process between the two ionic systems Be+H and BeH+. In addition, the vibrational energy level spacings are presented and compared with the available experimental and theoretical results. The permanent dipole moments for several electronic states of 1,3Σ+, 1,3 Π and 1,3 Δ symmetries are determined as function of the internuclear distance.