Thermal and electron-induced reactions of hydrazoic acid (HN3) adsorbed on gold and ice

The chemistry of hydrazoic acid (HN3) on polycrystalline gold and amorphous ice was studied as a function of HN3 exposure, temperature, and X-ray irradiation using reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). On Au, HN3 was found to adsorb molecularly at 100 K. In contrast, at 100 K the reaction of HN3 with ice was: dominated initially by deprotonation: and the formation of azide ions (N-3(-)). At higher HN3 exposures on ice, RAIRS data was consistent with molecular adsorption, although a distinct, more strongly bound molecular state was also observed that is attributed to hydrogen bonding between H2O and HN3. Annealing HN3 adsorbed on Au resulted in predominantly molecular HN3 desorption while in the HN3/ice system molecular desorption was accompanied by the production of ammonium azide (NH4+N3-). In contrast, NH4+N3- was not observed on the Au surface during annealing experiments. The formation of NH4+N3- is postulated to derive from the reactions of NH radicals, formed as a result of NN-NH bond-cleavage, within the adsorbate layer. In both the HN3/ice and HN3/Au systems, secondary electrons generated by X-ray irradiation induced NH4+N3- formation and nitrogen desorption, which are consistent with the following net reaction: 4HN(3(a)) --> NH4+N3(a)- + 4N(2(g))up arrow.