Articles you may be interested inThe dynamic effects on dissociation probability of H2-Pt(111) system by embedded atom method J. Appl. Phys. 109, 063509 (2011); 10.1063/1.3554690 Multiconfiguration time-dependent Hartree method applied to molecular dissociation on surfaces: H 2 + Pt ( 111 ) We have measured the sticking coefficient of H 2 on Pd͑111͒ as a function of incident translational energy, over the range 31-94 meV, and initial H 2 rotational state J, for Jϭ0 through Jϭ5, at a surface temperature of 423 K. These measurements test recent theoretical predictions that the H 2 /Pd sticking coefficient should decrease with increasing J, for low J, because more quickly rotating molecules are less easily ''steered'' to dissociation sites by interaction with the surface as they approach the metal ͓A. Gross, S. Wilke, and M. Scheffler, Phys. Rev. Lett. 75, 2718 ͑1995͔͒. We find that the sticking coefficient is sensitive to the rotational quantum number, first decreasing as J is raised from 0 to 3, then increasing again for Jϭ4 and 5. The greatest sensitivity found occurs for an incident translational energy of 73 meV, for which the sticking coefficient decreases from 0.76Ϯ0.05 for Jϭ0 to 0.54Ϯ0.13 for Jϭ3. In addition, we have found that a fraction of the H 2 incident in states Jϭ0 and Jϭ1 is excited to states Jϭ2 and Jϭ3, respectively, upon collision with the surface, with a probability that increases strongly with surface temperature and is roughly independent of incident translational energy. This rotational excitation does not result from dissociation followed by recombinative desorption, but occurs directly upon scattering from the surface. Furthermore, the majority of the excitation energy comes from the surface, and not from the incident translational energy of the molecule. The J-dependent sticking coefficients and the rotational excitation of the incident molecule by the surface are together strong evidence for a coupling between the surface and the rotational degree of freedom of the incident molecule, and support the model of dynamical steering in the adsorption process.

We have measured the survival probability of H2 in a single rovibrational state (v = 1, 1 = 1) scattering from a Cu(110) surface at 78 meV translational energy, using molecular beam and laser state preparation techniques.The integrated survival probability is found to be only 0.74~0.13, compared with 1.00 for the (v = O, J = 1) state. Possible loss channels for the vibrationally excited H2, including dissociation and inelastic scattering, are discussed. PACS numbers: 82.65.Pa, 34.50.Lf, 34.50.Pi, 68.35.Ja The hydrogen/copper system has become a prototype for studying activated dissociative adsorption for both experiment and theory [1,2]. On the experimental side, molecular beam studies of adsorption [3 -6] and laserbased studies of desorption [7,8] have gone a long way towards characterizing general trends in the translational, rotational, and vibrational state dependence of adsorption and desorption. On the theoretical side, advances have been equally impressive, with multidimensional first-principles potential energy surfaces being published [9 -12] and dynamical calculations on these surfaces verifying qualitatively the experimental trends. The dissociative adsorption of H2 on copper is thought to be dominated by vibrationally excited molecules at low ((0.4 eV) incident translational energy [1,2,4]. To explore this possibility, scattering experiments in which the translational and vibrational degrees of freedom of the molecule are controlled independently are needed. These results provide an important test of models for activated sticking and mode-specific surface dynamics.Several groups have used seeded molecular beams generated with heated nozzles to gain partially independent control over the translational and internal (rovibrational) excitation of the incident molecules [4,6]. Their studies demonstrated that internal excitation can be effective in overcoming the barrier to dissociative adsorption. In these studies, however, the incident molecules have thermal distributions of rovibrational states; this complicates interpretation of the results for individual states. Hodgson, Moryl, and Zhao [5] performed a heated nozzle experiment using laser-ionization detection to measure the survival probability of a selected rovibrational state.Again, however, a thermal distribution is present in their incident beam. In addition, they scale their measured reAectivity to the scattered ground state intensity to avoid integrating over the scattering angle.Here we present the first results of our scattering experiment using both laser state preparation and detection to gain true quantum state specificity. We report a measurement of the survival probability of H2 (v = 1, 1 = 1) scattered from Cu (110) at low incident translational energy (78 meV). Our measurement is absolute in that we have integrated the incident and scattered signal over 16 cm Cho Pulsed Nozzle Skl pie Probe Laser Beam mp Laser am ector Assembly FIG. 1. Schematic diagram of the experiment. A pulsed supersonic beam of Hq is incident normally on a Cu(11...

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We have observed the relaxation of H 2 from the rovibrational state ͑y 1, J 1͒ into (y 0, J 5, and J 7) upon scattering from Pd(111). The relaxation probability is 0.04 6 0.01 into J 5 and 0.03 6 0.01 into J 7. Relaxation does not occur when the surface is saturated with H atoms at low temperature. Furthermore, relaxation occurs with significant loss of vibrational energy, 50-120 meV, to the substrate. The relaxation mechanism is most likely electronically nonadiabatic. The survival probability of the incident H 2 ͑y 1, J 1͒ is 0.05 6 0.01 for a clean surface, but nearly unity for an H-saturated surface. [S0031-9007(97)04200-2] PACS numbers: 79.20.Rf

-As the photovoltaics (PV) industry has grown, the need for accurately monitoring the solar resource of PV power plants has increased. Historically, the PV industry has relied on thermopile pyranometers for irradiance measurements, and a large body of historical irradiance data taken with pyranometers exists. However, interest in PV reference devices is increasing. In this paper, we discuss why PV reference devices are better suited for PV applications, and estimate the typical uncertainties in irradiance measurements made with both pyranometers and PV reference devices. We assert that the quantity of interest in monitoring a PV power plant is the equivalent irradiance under the IEC 60904-3 reference solar spectrum that would produce the same electrical response in the PV array as the incident solar radiation. For PV-plant monitoring applications, we find the uncertainties in irradiance measurements of this type to be on the order of ±5% for thermopile pyranometers and ±2.4% for PV reference devices.