Baioui Née Koudjeti, Samira2021-04-082021-04-082020-01-01salle des thèsesDOC530-02-01https://dspace.univ-tlemcen.dz/handle/112/16301CsO et ses ions, méthode ab initio, méthode MRCI+Q, états électroniques, constantes spectroscopiques, moments dipolaires de transition, couplage spin-orbiteAfter having tested several bases relating to cesium and oxygen atoms and chosen those which allow to have results relatively in agreement with the experimental results, we studied the electronic states of the diatomic molecule CsO and of its CsO+ and CsOions, in the cases (a) and (c) of Hund. A high correlation ab initio computation was performed using the Molpro code, using the MRCI multiconfigurational method including Davidson's correction. The vibrational and rotational spectroscopic constants were calculated using the NUMEROV code. Satisfactory agreement was found between our results and the experimental results. The calculation of the spin-orbit couplings makes it possible to calculate the splitting of the potential energy curve at the equilibrium geometry. The calculation of the electronic transition moments between different states is used to study the stability of these systems. So we did these studies to the lowest molecular states. This work was carried out for the first time and can be used for further experimental studiesfr: CsO and its ions, ab initio method, MRCI+Q method, electronic states, spectroscopic constants, transition dipole moments, spin-orbit couplingThesis