TRANSIENT THIN-FILM LASER PYROLYSIS OF RDX

A new experimental technique is described for detecting initial pyrolysis products in rapidly heated condensed-phase energetic materials. A thin film sample is prepared by vapor deposition from a Knudsen oven onto a transparent substrate at 77 K. The film is heated to approximately 1000 K in 35 mus by irradiation with a pulsed CO2 laser. The sample and initial reaction products are then quenched to 77 K on a millisecond time scale by conduction of heat into the substrate. Reaction products are identified by their characteristic transmission FTIR spectra obtained after laser pyrolysis. Detection of the NO2 dimer molecule, N2O4, as an initial product in the thermal decomposition of condensed-phase RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) provides convincing evidence that the initial reaction step is homolysis of an N-N bond. No evidence is found for a competing concerted depolymerization pathway forming methylenenitramine, CH2NNO2.