Articles you may be interested inWater dissociation on Cu (111): Effects of molecular orientation, rotation, and vibration on reactivity J. Chem. Phys. 137, 094708 (2012); 10.1063/1.4749246Symmetry and rotational orientation effects in dissociative adsorption of diatomic molecules on metals: H2 and HD on Cu (111) Effects of translational, rotational, and vibrational energy on the dynamics of the D+H2 exchange reaction. A classical trajectory study J. Chem. Phys. 94, 7991 (1991); 10.1063/1.460133Effect of translational and vibrational energy on adsorption: The dynamics of molecular and dissociative chemisorption J.We have investigated the dependence on the rotational and vibrational states of the translational energy of D 2 (v,J) formed in recombinative desorption from Cu( 111). These results provide information about the effect of rotational energy relative to that of vibrational and translational energy on the dissociative chemisorption of D2 on Cu(lll). The range of rovibrational states measured includes rotational states J=0-14 for vibrational state v=O, J=0-12 for v= 1, and J=0-8 for v=2. D2 molecules were detected in a quantum-statespecific manner using three-photon resonance-enhanced multiphoton ionization (2+ 1 REMPI). Kinetic energies of desorbed molecules were obtained by measuring the flight time of Dt ions in a field-free region. The mean kinetic energies determined from these measurements depend strongly on the rotational and vibrational states. Analyzing these results using the principle of detailed balance confirms previous observations that vibrational energy is effective, though not as effective as translational energy, in promoting adsorption. Rotational motion is found to hinder adsorption for low rotational states (J < 5) and enhance adsorption for high rotational states (J> 5). Even for high J states, however, rotational energy is less effective than either vibrational energy, which is 30%-70% more effective than rotational energy, or translational energy, which is 2.5-3 times more effective than rotational energy in promoting adsorption. The measured internal state distributions for the rovibrational states listed above are consistent with the observed dependence of the kinetic energy of the desorbed molecules with the rotational state. In addition, the analysis performed yields the dependence of the adsorption probability on kinetic energy separately for each rovibrational state. These functions have very similar sigmoidal shapes for all states examined. Changing the quantum state is primarily associated with a shift in the position, or threshold energy, for the curves. The level at which these functions saturate or level off at high energy is independent of rotational state but varies nonmonotonically with the vibrational state. 8294

13. The crystallographic data for 1 are as folio~vs. Cell constants and an orientaton matrix for data collection cor-respond to the tr~cln~c space group p i , wth a = 12.903(3) A. 0 = 18.047(4) A, c = 9.341(4) A. n = 94.75(3)" p = 107.94(2)' y = 105.79(213, and i/ (cell volume) = 1958(l) A? There IS one molecule. Ci ,H,,i Si ,2B~2per unt cell (Z = I ) , givlng a formula weght of 1522.51 and a calculate density (D,l of 1.291 g ~m -~. The intensity data were collected through a glass capllary on a Rlgaku AFC5R dlffractometer w~th graphte-monochromated Mo-Ko: radiaton (h =

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Molecular beam t~hniq~es have ~~. used to study the dissociative chemisorption of nitrogen on W (1 ~ 0) .. ChemIsorptIOn probablhtles have been measured as a function of incidence angle ()~ ~d ~netIc energy E; surface coverage and temperature. In addition, angular scattering dlstnbutlons have been measured for a range of conditions and LEED has been used to examine surface structure. The initial (zero coverage limit) sticking probability is found to depend strongly on the incidence energy, scaling approximately with E " rather than with the velocity component normal to the surface. This probability is < 3 X 10-3 for E. <30 kJ mol-I and rises by more than a factor of 100 by-100 kJ mol-I, where it levels off a~-O. 35. It is ' argued that this behavior arises due to a strong chemical interaction prior to the barrier to di~soci~tion. Angular scatte~ng distributions revealed predominately quasispecular scattering With eVIdence as wen for a diffuse component at low energies. The sticking probability falls steadily with increasing surface coverage and a saturation coverage of-0.25 atomic ML is ?bserved for E;-10 kJ mol-I. At h~~er incidence kinetic energies, this saturation coverage Increases to-0.5 ML at 200 kJ mol. LEED structures are also reported, corresponding to coverages ofO.2S, 0.3, 0.5, and 0.52 ML. The 0.25 and 0.5 ML structures are identified as p(2X2) and c(4 X 2), respectively, for which structure models are proposed.

Angular variations in the kinetic energy of scattered species are found to provide a useful probe of the transition between gas-surface scattering regimes, complementing angular flux distributions. As incidence energies exceed a few eV, these change from being consistent with scattering from an extended target to being more typical of scattering from individual atoms. Results are presented for the Xe/Pt(l 11) system and are supported by detailed trajectory calculations.PACS numbers: 79.20.Rf An understanding of the dynamics of energy transfer at the gas-surface interface is required for detailed modeling of many different chemical and physical phenomena associated with this interface. These range from the trapping and sticking of atoms and molecules at relatively low en- ergies [1], to sputtering, plasma etching, and implantation at hyperthermal energies [2], Such knowledge is also of value in the design of spacecraft [3] and thermonuclear fusion reactors [4]. Molecular-beam scattering techniques offer a powerful tool for probing such interactionsand have been employed to examine many different systems. However, most studies have concerned angular distributions of scattered species for relatively low incidence energies, providing only a limited picture of the scattering dynamics. Since angular distributions reflect both the static corrugation of the gas-surface potential and differential momentum transfer parallel and perpendicular to the surface, velocity measurements are required for unambiguous interpretation. While high-energy collisions have been recognized as qualitatively distinct from those at low energy for many years [5-12], there is little experimental data that directly relate to the transition between these regimes.In this Letter we report results for the scattering of Xe from Pt(lll) which clearly show that variations in the energies of scattered species with scattering angle can be used to characterize the degree of penetration. At low incidence energies, ZT, < 1 eV, we find that the energies after scattering, £/, decrease with increasing scattering angle Of in a manner approximately consistent with parallel momentum conservation. At high energies, E,-> 5 eV, the opposite trend is observed, with E/ increasing with increasing final angle, in a manner consistent with scattering from one or more individual surface atoms. These qualitative conclusions are supported by detailed trajectory calculations.The molecular-beam surface scattering apparatus and the experimental techniques appropriate to this study have been described elsewhere [12][13][14]. The mounting of the Pt(l 11) crystal is such that thescattering plane intercepts the (111) face close to the [121] azimuth. Contamination levels are below our Auger detection limits (1%), sharp LEED patterns are obtained, and He scattering gives a specular peak width indistinguishable from the in-