Synthesis of OH from reaction of O and H on the Rh(100) surface

Article abstract of DOI:10.1063/1.453641

We report the synthesis of the OH intermediate from O and H coadsorbed on the Rh( 100) surface at 90 K and heated in ultrahigh vacuum ( UHV ) to between 140 and 240 K; the species is stable when cooled again to 90 K.When heated to higher than <*>240 K H2O is formed and evolved from the surface, demonstrating that OH formation is an important step in H20 synthesis.Temperature programmed electron energy loss spectroscopy (TP-EELS), temperature programmed reaction spectroscopy (TPRS), and low energy electron diffraction ( LEED ) were employed in the study of this intermediate.The EEL spectra of the OH species is characterized by a stretch mode at 394 meV, bending mode at 114 meV, frustrated lateral translation at 82 meV, and frustrated vertical translation at 54 meV.Off-specular measurements show that the OH bending mode is entirely dipole active at an impact energy of 6 eV.By monitoring the OH bend intensity normalized to the elastic intensity as the crystal temperature is linearly ramped, the kinetics of both OH synthesis and OH combination to form Hz0 was probed.Kinetics was obtained using the heating rate variation method (from the shift in the temperature of fastest reaction T_p with heating rate) and the coverage variation method ( from the shift in T_p resulting from different reactant concentrations ) .An activation energy of E_f = 4+/-1 kcal mol^-1 for OH formation was obtained.We find a half order coverage dependence indicating that OH formation occurs at the perimeters of O islands.An activation energy of E_c = 24+/-1 kcal/mol^-1 was obtained for the combination reaction.Isotopic substitution of deuterium ( D ) for hydrogen yielded no OD or D2O under UHV conditions, but an O covered surface heated in a D2 pressure <*>10^-8 Torr formed both surface OD and evolved D2O.This difference in H and D reactivity can be explained by the combination of the observed inverse kinetic isotope effect (KIE) in D2 recombinative desorption (in which D2 desorbs faster than H2) and the observed normal KIE in OD formation ( in which OD forms at a slower rate than OH ) .

Full text of DOI:10.1063/1.453641

Synthesis of OH from reaction of O and H on the Rh(100) surface
Bruce A. Gurney and W. Ho
Citation: The Journal of Chemical Physics 87, 5562 (1987); doi: 10.1063/1.453641
View online: http://dx.doi.org/10.1063/1.453641
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/87/9?ver=pdfcov
Published by the AIP Publishing
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