I n s i t u vibrational spectroscopy of specifically adsorbed azide on silver electrodes

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Abstract
In situ infrared vibrational spectra of azide ions specifically adsorbed on polycrystalline silver electrodes immersed in aqueous electrolytes of composition 1 to 30 mM azide and 0.1 M perchlorate are reported for the potential range 0.25 to 0 V vs Ag/AgCl (3 M KCl). Adsorbed azide was not detected spectroscopically between 0 and −0.9 V, a range known from differential capacitance measurements to allow adsorption onto the silver electrodes. These experimental observations have been interpreted with the help of ab initio calculations of the vibrational frequencies of [AgN3]0 and [AgN3]− for two configurations with C∞v and C2v symmetries representing simple models for azide adsorbed with its configuration axis perpendicular and parallel to the electrode surface, respectively. Besides the charge states specified, calculations are also reported for static applied fields along the symmetry axis. Taken together, the experiments and calculations support a model in which azide adsorbs oriented perpendicular to the surface at the higher surface concentrations induced by potentials more positive than OV, and is adsorbed with long axis parallel to the surface at negative potentials.

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