Hamid Berriche - Academia.edu (original) (raw)

Papers by Hamid Berriche

The electronic structure of BeSe and BeTe molecules has been investigated using the ab initio CAS... more 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 , ω e , and B e , and the dissociation energy D e are determined in addition to the vertical transition energy T v. 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.

Russian Journal of Physical Chemistry A, 2017

Calculations of the adiabatic potential energy curves and the transition dipole moments between t... more Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (X 1 Σ +) and the first excited (A 1 Σ +) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs + , Li + and Na + cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A 1 Σ + state using the Franck-Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A 1 Σ + state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.

The European Physical Journal D, 2016

The transition dipole moments of the first eight 1 Σ + states of the LiH molecule have been calcu... more The transition dipole moments of the first eight 1 Σ + states of the LiH molecule have been calculated using ab initio approach based on the pseudopotential technique. Such transition dipole moments have been used to determine the radiative lifetimes for all vibrational levels of the first and the second excited states, A and C 1 Σ + , using accurate adiabatic potential energy curves. In addition to the bound-bound transitions, we have included the bound-free emissions probabilities. The latter was calculated exactly and using the Franck-Condon approximation and then included in the total radiative lifetime. A significant change in these lifetimes has been observed, particularly for the higher excited vibrational levels for which the approximate evaluation breaks down. The radiative lifetimes of the vibrational levels of the A 1 Σ + exited sate are in very good agreement with the few available theoretical and experimental results. However, the radiative lifetimes associated to the C 1 Σ + state are presented here for the first time.

Journal of Molecular Structure: THEOCHEM, 2004

The potential energy surface describing the interaction between the hydrogen atom and the rotatin... more The potential energy surface describing the interaction between the hydrogen atom and the rotating LiH molecule has been calculated very accurately and presented in our previous work (J. Mol. Struct. (THEOCHEM) 678 (2004) 11). The rigid rotor potential already fitted analytically and expanded in terms of Legendre polynomials, is employed here to evaluate the pure state-to-state rotational cross-sections over a range of energies of astrophysical interest varying from 10 to 3000 cm 21. An exact close coupling and CS calculation of the state to state rotational cross-section was done first in the range of small energy, from 10 to 100 cm 21. The comparison of both results shows the good agreement between them and leads to a generalisation of such calculation for higher energy using the CS approximation. We determine the state to state rotational cross-section for transitions from j ¼ 0; 1, 2, 3, 4 to all accessible final states j 0 ; at total energy varying between 10 and 3000 cm 21. The presented cross-sections were found to be very large even for low energy and large D jj 0 : Thus indicates the important probability to produce the heated LiH molecule in excited states by collisions with H and explain the strong anisotropy discussed in our previous paper.

Journal of Quantitative Spectroscopy and Radiative Transfer, 2016

Line shapes for the Rb D 1 (5 2 S 1=2 25 2 P 1=2) and D 2 (5 2 S 1=2 25 2 P 3=2) transitions with... more Line shapes for the Rb D 1 (5 2 S 1=2 25 2 P 1=2) and D 2 (5 2 S 1=2 25 2 P 3=2) transitions with 4 He and 3 He collisions at pressures of 500-15,000 Torr and temperatures of 333-533 K have been experimentally observed and compared to predictions from the Anderson-Talman theory. The ground X 2 Σ þ 1=2 and excited A 2 Π 1=2 , A 2 Π 3=2 , and B 2 Σ þ 1=2 potential energy surfaces required for the line shape predictions have been calculated using a one-electron pseudo-potential technique. The observed collision induced shift rates for 4 He are dramatically higher for the D 1 line, 4.60 7 0.12 MHz/Torr, than the D 2 line, 0.20 7 0.14 MHz/ Torr. The asymmetry is somewhat larger for the D 1 line and has the same sign as the shifting rate. The 3 He broadening rate for the D 2 line is 4% larger than the 4 He rate, and 14% higher for the D 1 line, reflecting the higher relative speed. The calculated broadening rates are systematically larger than the observed rates by 1.1-3.2 MHz/Torr and agree within 14%. The primary focus of the current work is to characterize the high pressure line shapes, focusing on the non-Lorentzian features far from line center. In the far wing, the cross-section decreases by more than 4 orders of magnitude, with a broad, secondary maximum in the D 2 line near 735 nm. The potentials do not require empirical modification to provide excellent quantitative agreement with the observations. The dipole moment variation and absorption Boltzmann factor is critical to obtaining strong agreement in the wings.

Journal of Molecular Structure: THEOCHEM, 2003

The potential energy curves and the spectroscopic constants of the molecular ion LiNa þ electroni... more The potential energy curves and the spectroscopic constants of the molecular ion LiNa þ electronic states dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s and 4p) þ Na þ and Li þ þ Na(3s, 3p, 4s, 4p, 5s and 4d) are calculated using an ab initio approach involving a non-empirical pseudopotential for the Li (1s 2) and Na (1s 2 2s 2 2p 6) cores and core-valence correlation correction. A very good agreement has been obtained for the ground state for the spectroscopic constants with the available theoretical and experimental works. On the other hand for several excited states a clear discrepancy between this study and the model potential work of Magnier et al. [J. Phys. Chem. A 105, 2001] is observed. They found that the 2, 4, 6, 8, 10 2 S and 4 2 P states are dissociative although they are in our work attractive with potential wells of some hundreds of cm 21 .

Journal of Molecular Structure: THEOCHEM, 2006

The evaluation of the first and second derivative of the non adiabatic coupling between the sever... more The evaluation of the first and second derivative of the non adiabatic coupling between the several 1 R + adiabatic states of LiH, RbH and CsH molecules, is considered from accurate diabatic and adiabatic data. Such derivatives of the electronic wave function are determined through a numerical differentiation of the rotational matrix connecting the diabatic and adiabatic representations. The first as well as the second derivative presents many peaks, related to ionic-neutral and neutral-neutral coupling between the 1 R + states. Such radial coupling has been exploited to calculate the first adiabatic correction, which corresponds to the diagonal term of the second derivative divided by the reduced mass, for the ground and some excited states of the three molecules. The second adiabatic correction has been determined using the Virial theorem. The first adiabatic correction was added to the adiabatic potential energy curves to re-determine the corrected spectroscopic constants and vibrational energy levels. The vibrational shift, which is the difference between the corrected and the adiabatic levels, has been calculated for X, A, C and D 1 R + states of the three molecules. A shift of some 10 cm À1 is observed for some vibrational levels showing the breakdown of the Born-Oppenheimer approximation.

Journal of Cluster Science, 2014

Your article is protected by copyright and all rights are held exclusively by Springer Science +B... more Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Journal of Molecular Structure: THEOCHEM, 2007

Using an ab initio approach involving a non-empirical pseudopotentials for Na and Rb atoms, the a... more Using an ab initio approach involving a non-empirical pseudopotentials for Na and Rb atoms, the adiabatic potential energy curves of 26 electronic states of NaRb + ionic molecule dissociating up to Na(4p) + Rb + and Na + + Rb(7s) have been investigated. Their molecular spectroscopic constants have been derived and compared with the available theoretical works. Furthermore, the transition dipole moments from X 2 R + and 2 2 R + to higher excited states have been determined. Numerous avoided crossings between electronic states of 2 R + and 2 P symmetries have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Na + Rb and NaRb +. The accurate potential energy curves have been exploited to realize a long-range vibrational level spacing analysis using the WKB semi-classical approximation in order to extract the Na and Rb atomic static dipole polarizabilities. A very good agreement between our static dipole polarizabilities and the available experimental and theoretical works has been observed.

Physics Procedia, 2009

We have studied the structure and the stability of the ionic Na + Kr n and neutral NaKr n (n=1-25... more We have studied the structure and the stability of the ionic Na + Kr n and neutral NaKr n (n=1-25) small clusters. The potential energy surface of the cluster is described using additive potentials, which represent the pair interactions taken from the best available CCSD ab initio calculations. The V Na+Kr ,V Kr-Kr potentials have been fitted, respectively, by Tang and Toennies and Lennard-Jones (LJ) forms, while the V NaKr is presented by a modified HFD analytical potential obtained by a fully quantummechanical approach based on very accurate spectroscopic data. In addition, the potential energy surface has been explored by the Monte Carlo Basin Hopping method in order to determine the geometry of Na + Kr n and NaKr n clusters and their isomers. Their relative stability was studied by evaluating the energy per Krypton atom and the energy differences as function of number n of Krypton atoms in clusters. It was shown, for Na + Kr n , that n = 6, 8, 10, 16 and 20 are the most stable structures, which is in good agreement with the previous experimental results.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Journal of Molecular Spectroscopy, 2005

The adiabatic potential energy, the spectroscopic constants and the transition dipole moments of ... more The adiabatic potential energy, the spectroscopic constants and the transition dipole moments of the lowest electronic states of the LiK + molecule, dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s, and 4p) + K + and Li + + K(4s, 4p, 5s, 3d, 5p, 4d, and 6s), have been investigated. We have used an ab initio approach involving a non-empirical pseudopotential for the Li (1s 2) and K (1s 2 2s 2 2p 6 3s 2 3p 6) cores and core valence correlation correction. A very good agreement has been obtained for the ground state for the spectroscopic constants with the available theoretical works. The transition dipole moment from X 2 R, 2 2 R, 3 2 R, and 4 2 R states to higher excited states have been determined. Numerous avoided crossing between electronic states of 2 R and 2 P symmetries, have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Li + K and LiK + .

The Journal of Chemical Physics, 1997

Accurate positions and nonradiative lifetimes of states belonging to the adiabatic A state of LiH... more Accurate positions and nonradiative lifetimes of states belonging to the adiabatic A state of LiH are estimated. The results coming from a Golden Rule treatment in the adiabatic scheme present excellent agreement with those obtained through a diabatic close coupling calculation. That confirms the accuracy reached in both approaches and also in the treatment of the diabatic–adiabatic transformation. It involves, in particular, an effective phase control that is needed to properly estimate nonadiabatic couplings. Also, a powerful numerical procedure to obtain energy profiles in the diabatic close coupling frame is described and applied in this work.

Computational Materials Science, 2007

A vibrational level spacing analysis of the lowest electronic states of the LiK + ionic molecule ... more A vibrational level spacing analysis of the lowest electronic states of the LiK + ionic molecule dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s and 4p) + K + and Li + + K(4s, 4p, 5s, 3d, 5p, 4d, 6s) has been performed using the usual WKB semiclassical approximation. Accurate long-range potentials have been determined and allowing for the determination of all vibrational levels near the dissociation limit, the Li and K atomic polarizabilities, the number of trapped vibrational levels, and the vibrational turning points. The extracted polarizabilities for the ground levels of Li and K atoms have been compared with the available theoretical and experimental values. A very good agreement has been shown for them. The obtained atomic polarizabilites have been used to reproduce the long-range potential energy curves showing the good agreement between the ab initio calculated and the analytical potentials. A systematic generation of the missed Numerov vibrational levels and their turning points near the dissociation limit was done for all the LiK + electronic states.

Chemical Physics Letters, 1995

The permanent dipole moments of the eight low-lying 1£ states of the LiH molecule are calculated ... more The permanent dipole moments of the eight low-lying 1£ states of the LiH molecule are calculated by an ab initio approach for both the adiabatic and the diabatic representations. The results shed light on the interplay between the ionic and the neutral states producing a direct illustration of the ionic character of the electronic wavefunction. Our results suggest that the location and the width of the avoided crossings for the potential energy curves could be experimentally derived.

Molecular Physics, 2018

In this theoretical work, we calculate potential energy curves, spectroscopic parameters and tran... more 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 Journal of Physical Chemistry A, 2015

Dissociative photoionization of the He•••Li 2 van der Waals complex to the ground electronic stat... more Dissociative photoionization of the He•••Li 2 van der Waals complex to the ground electronic state of the He•••Li 2 + ion is investigated theoretically. The photoionization cross section is computed using existing interaction potentials. Resonances are found on top of a structured continuum. They are assigned to vibrational predissociation of the ion by comparison with Fermi Golden Rule calculations. Because of the differences in potential energy surfaces between the neutral and ionic complexes, only the resonances corresponding to quasibound states with the highest excitation in the van der Waals modes are visible. The other quasi bound states obtained in the Fermi Golden Rule calculations can give information on vibrational energy relaxation rates in other collisional processes involving the lithium dimer ion and a helium atom.

New Journal of Physics, 2020

Experiments with cold ion–atom mixtures have recently opened the way for the production and appli... more 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 ...

Journal of Physics B: Atomic, Molecular and Optical Physics, 2016

We study theoretically interaction potentials and low energy collisions between different alkali ... more 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.