Vibrational characterization of NH and NH2 reaction intermediates on the Ru(11(2)over-bar-0) surface

NH and NH2 reaction intermediates were prepared on the Ru(11 (2) over bar0) surface by thermal dehydrogenation of NH3 and studied using high-resolution electron energy-loss spectroscopy. NH2 and NH were isolated to a high degree, which allows to unambiguously identify their vibrational modes. From isotope experiments with (ND3)-N-15, frustrated translational and rotational (bending, rocking) modes were differentiated. NH2 exhibits a scissoring mode at 189.7 meV, a rocking mode at 165.4 meV and translational modes at 62.2 and 44.3 meV. NH2 is tilted relative to the surface normal within an adsorbate complex of C-s symmetry. For NH two rather low-lying bending modes at 83.2 and 88.2 meV were identified due to NH species presumably adsorbed in the two different threefold-hollow sites within the Ru(1 12 0)(l x 1) unit cell, also in a tilted geometry. A long-standing wrong assignment of the NH bending mode could be corrected. (C) 2002 Published by Elsevier Science B.V.