arXiv subjects

Hamid Berriche

Publications and source records attributed to Hamid Berriche.

6 recordsLinked to original sources

arXiv2026

Diatomic molecular anions of alkali-metal and alkaline-earth-metal atoms

Studies of anions are inherently more challenging than investigations of neutrals and cations because of the diffuse and weakly bound character of an anionic electron. Here, we present a comprehensive computational examination of ground-state diatomic molecular anions composed of alkali-metal (Li, Na, K, Rb, Cs, Fr) and alkaline-earth-metal (Be, Mg, Ca, Sr, Ba, Ra) atoms. We study 21 alkali-metal diatomic anions in the X$^{2}\Sigma^{+}$ electronic state and 36 alkali-metal--alkaline-earth-metal diatomic anions in the X$^{1}\Sigma^{+}$ electronic state. The calculations employ a hierarchy of the coupled cluster methods, combined with large Gaussian basis sets and small-core relativistic energy-consistent pseudopotentials for heavier elements. We compute potential energy curves, permanent electric dipole moments, and static polarizabilities, and we assess convergence and uncertainties of our results. Additionally, using the multireference configuration interaction and equation-of-motion electron-attachment coupled cluster methods, we investigate excited electronic states of alkali-metal molecular anions, including valence-bound and dipole-bound states. We predict crossings between ground neutral and excited anionic states, which may enhance resonant electron attachment and subsequent anion dissociation. This finding may be relevant for experiments with mixtures of ultracold ground-state alkali-metal molecules and Rydberg atoms.

physics.atom-ph↗

arXiv2022

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 $^{1,3}Σ^+$, $^{1,3}Π$ and $^{1,3}Δ$ symmetries are determined. Furthermore, we identify the avoided crossings between the electronic states of $^{1,3}Σ^+$ and $^{1,3}Π$ 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.

physics.atom-ph↗

arXiv2020

Ab initio electronic structure and prospects for the formation of ultracold calcium--alkali-metal-atom molecular ions

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 pseudopotential, 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.

physics.atom-ph↗

arXiv2018

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$Σ^+$, 1,3$Π$ and 1,3$Δ$ 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.

physics.atom-ph↗

arXiv2018

Spectroscopic properties of the molecular ions BeX^+ (X=Na, K, Rb): Forming cold molecular ions from an ion-atom mixture by stimulated Raman adiabatic process

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.

physics.atom-ph↗

arXiv2016

Interactions and low energy collisions between an alkali ion and an alkali atom of different nucleus

We study theoretically interaction potentials and low energy collisions between different alkali atoms and alkali ions. Specifically, we consider systems like X + Y$^{+}$, where X(Y$^{+})$ is either Li(Cs$^+$) or Cs(Li$^+$), Na(Cs$^+$) or Cs(Na$^+$) and Li(Rb$^+$) or Rb(Li$^+$). We calculate the molecular potentials of the ground and first two excited states of these three systems using pseudopotential method and compare our results with those obtained by others. We derive ground-state scattering wave functions and analyze cold collisional properties of these systems 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 needs to take into account at least 60 partial waves. Low energy scattering properties calculated in this paper may serve as a precursor for experimental exploration of quantum collisions between an alkali atom and an alkali ion of different nucleus.

physics.atom-ph↗