The main goal of this thesis is to explore theoretically, on the example of the RbCs molecule, the formation, by optical means, of heteronuclear dialkali molecules in the lowest vibrational level of the ground electronic state, starting from ultracold atom pairs. The bound spectrum and the continuum close to threshold of the ground and lowest triplet electronic states are analyzed together with the levels 0+, 0- and 1 below the Rb(5s)Cs(6p 1/2) limit. A 'universal' description of the profiles of shape resonances, valid for any diatomic molecule, points out the crucial role of the s-wave scattering length. Calculations of Franck-Condon factors (FCF) relevant to photoassociation (PA) and spontaneous radiative decay (RS) are presented, showing, in agreement with experiment, that the v=37 level of the triplet electronic state is most favorably populated after PA followed by RS. The so-called 'resonant' coupling is examined in great detail, underlying its crucial influence on PA and RS. Radiative lifetimes are systematically calculated. The FCF associated with optical two-color population transfer from the triplet v=37 level toward the absolute ground level are also calculated, showing that the path through levels of 0+ symmetry is the most efficient. The possibilities offered by femtosecond sources for the population transfer toward deeply bound levels are explored and the dynamics is analyzed, from the low field up to the high field regime. Trains of femtosecond pulses are considered. The Mapped Fourier Grid Hamiltonian method, cornerstone of this study, proves its efficiency to accurately analyze the dynamics of transition processes between bound and scattering levels.