Nitrides such as Si3N4 and GaN are made by the reaction of the respective oxide with N2 or NH3. In order to understand the mechanism of formation of nitrides, reactive laser ablation of B2O3, Al2O3, Ga2O 3, and SiO2 in pure form, as well as in mixture with carbon, has been carried out in an atmosphere of nitrogen or ammonia in a pulsed supersonic jet. The reaction of N2 with SiO2 gives nitridic species such as Si2Ny (y≤5) in the vapor phase. On reaction with N2 in the presence of carbon, B 2O3 and Ga2O3 yield species of the type BxNy and GaNy, respectively. Nitridic species are preponderant in the reaction with ammonia only in the case of SiO2. Al2O3 predominantly gives oxynitridic species under the reaction conditions examined. © 2004 Elsevier Ltd. All rights reserved.