Vibrational characterization of NH and NH2 reaction intermediates on the Ru(1 1 2̄ 0) surface

NH and NH2 reaction intermediates were prepared on the Ru(1 1 2̄ 0) 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 15ND3, 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 Cs 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 1 2̄ 0)(1×1) unit cell, also in a tilted geometry. A long-standing wrong assignment of the NH bending mode could be corrected.