Interaction of HNCO with Au(111) surfaces

The surface chemistry of isocyanic acid, HNCO, and its dissociation product, NCO, was studied on clean, O-dosed and Ar ion bombarded Au(111) surfaces. The techniques used are high resolution energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). The structure of Ar ion etched surface is explored by scanning tunneling microscopy (STM). HNCO adsorbs molecularly on Au(111) surface at 100K yielding strong losses at 1390, 2270 and 3230cm−1. The weakly adsorbed HNCO desorbs in two peaks characterized by Tp=130 and 145K. The dissociation of the chemisorbed HNCO occurs at 150K to give NCO species characterized by a vibration at 2185cm−1. The dissociation process is facilitated by the presence of preadsorbed O and by defect sites on Au(111) produced by Ar ion bombardment. In the latter case the loss feature of NCO appeared at 2130cm−1. Isocyanate on Au(111) surface was found to be more stable than on the single crystal surfaces of Pt-group metals. Results are compared with those obtained on supported Au catalysts. Effects of HNCO exposure on the HREEL spectra of Au(111) at ~100K. [Display omitted] ► The chemistry of HNCO and NCO on Au(111) surface. ► Dissociation of HNCO on Au(111) promoted by preadsorbed O atoms. ► Generation of active sites on Au(111) surface by Ar+ ion sputtering.