From the spectroscopic study of the Ti, Ti2 + N2O reaction products trapped in rare gas matrices, we were able to identify three products for the reaction Ti + N2O (a simple van der Waals adduct, an end-on complex and a side-on molecule), and two for the 3Ti2 + N2O = 1[OTi2(η1 - NN)] or 1[OTiNTiN] reaction. We showed that the atomic titanium is unreactive with respect to N2O in its ground state, while the titanium dimer spontaneously reacts with N2O leading to the N-O bond scission and yielding to an intermediate adduct 1[OTi2(η1 - NN)]. A second bond breaking, the N-N bond cleavage, could be achieved by means of photochemistry, leading to the final product 1[OTiNTiN]. Over all the available functionals, none of them has been shown to systematically overshadow all the others. However, difficulties lie in choosing, from the plethora of density functionals, the one to apply. The selection of the functional to use depends on the problem at hand, i.e., on both the dispersion and static correlations. In this thesis, a strategy has been suggested in order to select the most adequate functional. It consists of a validation of calculation method for a given system by reproducing a set of reference data, obtained either by experiment or at the CCSD(T) or CASPT2 levels on the structural, energetic and vibrational properties.
