Infrared laser-induced decomposition of GAP

Abstract

The laser-induced decomposition of a solid azido polymer (GAP) is reported. A TEA CO 2 laser (tunable in the 920–1080 cm −1 range) is used and the dissociation yield is shown to correlate with the one photon absorption spectrum, although about 15 photons per molecule are required to break the weakest bond. At high laser fluence, complete decomposition of the whole sample can be affected using a single laser pulse, leading mostly to gaseous products. When irradiated under vacuum using medium laser fluence (up to 5 J/cm 2), only a small fraction of the polymer dissociates and the main gaseous products are N 2, CO, C 2H 4, HCN, and probably H 2. Many other products are formed in much lesser yields, but two compounds— formaldehyde and ammonia—that have been reported as major products upon thermal decomposition, are absent. In addition a powdery polymeric material containing a CHNH group is formed. The overall yield is roughly proportional to the laser pulse energy in the range 30–150 mJ (corresponding to about 1–5 J/cm 2). Addition of helium or oxygen leads to a dramatic reduction in the HCN relative yield and a smaller reduction of acetylene yield with little change in other major products yields and to the formation of a sticky amber colored polymer. The results are consistent with the initial rupture of a NN 2 bond of the azido group, followed by creation of reactive species that lead to the formation of the solid polymer and the final gaseous products. The effect of added gases is presumably cooling of these primary reactive species.