Thermal and Electron-Induced Reactions of Hydrazoic Acid (HN3) Adsorbed on Gold and Ice

The chemistry of hydrazoic acid (HN 3 ) on polycrystalline gold and amorphous ice was studied as a function of HN 3 exposure, temperature, and X-ray irradiation using reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). On Au, HN 3 was found to adsorb molecularly at 100 K. In contrast, at 100 K the reaction of HN 3 with ice was dominated initially by deprotonation and the formation of azide ions (N 3 - ). At higher HN 3 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 H 2 O and HN 3 . Annealing HN 3 adsorbed on Au resulted in predominantly molecular HN 3 desorption while in the HN 3 /ice system molecular desorption was accompanied by the production of ammonium azide (NH 4 + N 3 - ). In contrast, NH 4 + N 3 - was not observed on the Au surface during annealing experiments. The formation of NH 4 + N 3 - 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 HN 3 /ice and HN 3 /Au systems, secondary electrons generated by X-ray irradiation induced NH 4 + N 3 - formation and nitrogen desorption, which are consistent with the following net reaction: 4HN 3(a) → NH 4 + + 4N 2(g) ↑