Signatures of site-specific reaction of H2 on Cu(100)

Abstract

Six-dimensional quantum dynamical calculations are presented for the reaction of (v, j) H 2 on Cu͑100͒, at normal incidence, for vϭ0 -1 and jϭ0 -5. The dynamical calculations employed a potential energy surface computed with density functional theory, using the generalized gradient approximation and a slab representation for the adsorbate-substrate system. The aim of the calculations was to establish signatures from which experiments could determine the dominant reaction site of H 2 on the surface and the dependence of the reaction site on the initial rovibrational state of H 2 . Two types of signatures were found. First, we predict that, at energies near threshold, the reaction of (vϭ1) H 2 is rotationally enhanced, because it takes place at the top site, which has an especially late barrier and a reaction path with a high curvature. On the other hand, we predict the reaction to be almost independent of j for (vϭ0) H 2 , which reacts at the bridge site. Second, we predict that, at collision energies slightly above threshold for which the reaction probabilities of the (vϭ0) and (vϭ1) states are comparable, the rotational quadrupole alignment of (vϭ1) reacting molecules should be larger than that of (vϭ0) reacting molecules, for jϭ1, 4, and 5. For ( j ϭ2) H 2 , the opposite should be true, and for ( jϭ3) H 2 , the rotational quadrupole alignment should be approximately equal for (vϭ1) and (vϭ0) H 2 . These differences can all be explained by the difference in the predicted reaction site for (vϭ1) and (vϭ0) H 2 ͑top and bridge͒ and by the differences in the anisotropy of the potential at the reaction barrier geometries associated with these sites. Our predictions can be tested in associative desorption experiments, using currently available experimental techniques.

Reactive scattering of H2 from Cu(100): Comparison of dynamics calculations based on the specific reaction parameter approach to density functional theory with experiment

“…Impact on the top site has been found to be relevant for vibrationally inelastic scattering and for dissociation of vibrationally excited and highly rotationally excited H 2 on Cu(100). 40,46,57 The 2D elbow for this dissociation route shows a large curvature of the reaction path and an especially late barrier (occurring at a large H-H distance r, see Fig. 3 and Table I).…”

“…45 The system was also used to uncover experimental signatures of site reactivity in work bearing a close relationship to the present work, as the suggested experimental signature involves the relationship between measured rotational quadrupole alignment parameters of H 2 (v = 0, j) and (v = 1, j) just above the reaction threshold. 46, 47 H 2 + Cu(100) was also used as a benchmark to demonstrate a new, symmetry adapted pseudospectral method. 48 Finally, more recently the system has been used to explore the applicability of a mean field quantum dynamics method to investigate the effect of phonons on reactive and non-reactive scattering of H 2 from copper surfaces.…”

Theoretical Study of Hydrogen Adsorption on Ruthenium Clusters

“…Many previous researches showed that the catalytic properties of clusters are structure dependent, leading to different adsorption energies and sites for different structures of clusters [1][2][3][4][5][6]. Hydrogen is employed in many modern technologies [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], so surface reactions of hydrogen molecules in transition metals have been carried out over the adsorption and desorption of hydrogen and deuterium molecules on well-defined single crystal metals. Axel Pramann et al [22] studied hydrogen chemisorption rates and electronic structures of small Nb n Al -clusters by photoelectron spectroscopic method.…”

Away from generalized gradient approximation: Orbital-dependent exchange-correlation functionals

“…Such a preference is often seen in activated reactions at low collision energies and arises because the anisotropy of the PES is generally large in the polar angle, leading to enhanced reaction due to rotational deexcitation of rotational states with low ͉m J ͉. 39,52 This is also the likely cause in this case: the ͑J =2, m J =0͒ state can deexcite, freeing some energy to overcome any low barriers encountered. In addition, the ͑J =2, m J =2͒ state is more tilted with respect to the surface plane than helicopter states for higher J. Helicoptering molecules for J = 2 are thus less favorably aligned to react than they are for higher initial rotational states.…”

“…5͑a͔͒. 16,32,[37][38][39] In the HE range, the dissociation is predominantly direct in nature, while in the LE range the direct and indirect components both contribute ͓Fig. 5͑b͔͒.…”