Electronic structure, spectroscopy, cold ion-atom elastic collision properties and photoassociation formation prediction of (MgCs)+^+ molecular ion

Studies on the interactions between an alkali atom and an alkaline earth ion at low energy are important in the field of cold chemistry. In this paper we, extensively, study the structure, interactions, and dynamics of (MgCs)$^+$ molecular ion. We use an ab initio approach based on the formalism of non-empirical pseudo-potential for Mg$^{2+}$ and Cs$^+$ cores, large Gaussian basis sets and full valence configuration interaction. In this context, the (MgCs)$^+$ cation is treated as an effective two-electron system. Potential energy curves and their spectroscopic constants for the ground and the first 41 excited states of $^{1,3}\Sigma^+$, $^{1,3}\Pi$ and $^{1,3}\Delta$ symmetries are determined. Furthermore, we identify the avoided crossings between the electronic states of $^{1,3}\Sigma^+$ and $^{1,3}\Pi$ symmetries. These crossings are related to the charge transfer process between the two ionic limits Mg/Cs$^+$ and Mg$^+$/Cs. In addition, vibrational-level spacings, the transition and permanent dipole moments are presented and analysed. Using the produced potential energy data, the ground-state scattering wave functions and elastic cross sections for a wide range of energies are performed. Furthermore, we predict the formation of translationally and rotationally cold molecular ion (MgCs) + in the ground state electronic potential energy by stimulated Raman type process aided by ion-atom cold collision. In the low energy limit (< 1 mK), elastic scattering cross sections exhibit Wigner law threshold behaviour; while in the high energy limit the cross sections as a function of energy E go as E$^{-1/3}$. A qualitative discussion about the possibilities of forming the cold (MgCs)$^+$ molecular ions by photoassociative spectroscopy is presented

Structure, spectroscopy and cold collisions of the (SrNa)+^+ ionic system

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

Transition dipole function and radiative lifetimes for the A and C 1Σ+ states of the LiH molecule

International audienc

Structure and spectroscopic properties of the beryllium hydride ion BeH

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 (2s2, 2s2p, 2s3s, 2p2, 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+,  1,3Π and  1,3Δ 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  1,3Π 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+,  1,3Π and  1,3Δ symmetries are determined as function of the internuclear distance

Structure and stability of small Li

We have studied the structure and stability of the Li2+(X2Σ+g)Xen (n = 1–6) clusters for special symmetry groups. The potential energy surfaces of these clusters, are described using an accurate ab initio approach based on non-empirical pseudopotential, parameterized l-dependent polarization potential and analytic potential forms for the Li+Xe and Xe-Xe interactions. The pseudopotential technique has reduced the number of active electrons of Li2+(X2Σ+g)-Xen (n = 1–6) clusters to only one electron, the Li valence electron. The core-core interactions for Li+Xe are included using accurate CCSD(T) potential fitted using the analytical form of Tang and Toennies. For the Xe-Xe potential interactions we have used the analytical form of Lennard Jones (LJ6 - 12). The potential energy surfaces of the Li2+(X2Σ+g)Xen (n = 1–6) clusters are performed for a fixed distance of the Li2+(X2Σ+g) alkali dimer, its equilibrium distance. They are used to extract information on the stability of the Li2+(X2Σ+gXen (n = 1–6) clusters. For each n, the stability of the different isomers is examined by comparing their potential energy surfaces. Moreover, we have determined the quantum energies (D0), the zero-point-energies (ZPE) and the ZPE%. To our best knowledge, there are neither experimental nor theoretical works realized for the Li2+(X2Σ+gXen (n = 1–6) clusters, our results are presented for the first time

Electronic structure and spectra of the RbHe van der Waals system including spin orbit interaction

The potential energy interaction, the spectroscopic properties and dipole functions of the RbHe van der Waals dimer have been investigated. We used a one-electron pseudopotential approach and large Gaussian basis sets to represent the two atoms Rb and He. The Rb+ core and the electron-He interactions were replaced by semi-local pseudopotentials and a core-core interaction is included. Therefore, the number of active electrons of RbHe is reduced to only one electron. Consequently, the potential energy curves and dipole moments for many electronic states dissociating into Rb(5s,5p,4d,6s,6p,5d,7s)+He are performed at the SCF level. In addition, the spin-orbit coupling is included in the calculation. The Rb+He interaction, in its ground state, is taken from accurate CCSD (T) calculations and fitted to an analytical expression for a better description of the potential in all internuclear ranges. The spectroscopic properties of the RbHe electronic states are extracted. The comparison of these constants has shown a very good agreement for the ground state as well as for the lower excited states when compared with existing theoretical and experimental studies