The purely “fast” distribution of H2 and D2 molecules desorbing from Cu(100) and Cu(111) surfaces

Comşa, George; David, Rudolf

doi:10.1016/0039-6028(82)90487-3

Cited by 217 publications

(78 citation statements)

References 14 publications

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“…These are dynamic effects observed, for example, for the hydrogenlcu system (8)(9)(10)(11)39). They are most likely to occur if the desorption process is correlated with a change in the bond length of the desorbing molecule and if there is a barrier in the reaction path for desorption.…”

Section: Discussionmentioning

confidence: 99%

Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

Bracker¹,

Jakob²,

Näher³

et al. 1994

Can. J. Chem.

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, 643 (1994). The dry etching reaction of solid copper surfaces with fluorine atoms or molecules has been studied with laser-induced fluorescence spectroscopy. The reaction product, copper monofluoride, CuF, is produced in the X'C+ electronic ground state and desorbs into the gas phase at surface temperatures above approximately 750 K. Rotationally resolved LIF excitation spectra of the C ' n + XIC+ band system of CuF molecules desorbing from an isotopically purified 6 ' C~ polycrystalline sample are obtained under conditions of coherent saturation. From the product state analysis it is deduced that the rovibrational product populations are in thermal equilibrium with the surface. The same holds for the translational velocity distribution obtained by Doppler-shift measurements. A pronounced polarization effect, particularly strong for Q branch transitions, can be traced back to photoselection of single-parity levels in the A doublets of the C l n state. A theoretical analysis for the distribution of J vectors, based on the formalism of Greene and Zare, shows that the measured degree of polarization is quantitatively in agreement with an isotropic distribution of rotational angular momentum vectors. The vibrational and translational product equilibration is not affected by changing the reactants from F2 molecules to F atoms, which increases the exoergicity of the overall reaction. The results are interpreted in terms of the absence of a barrier for desorption and a long residence time of the chemisorbed CuF molecules at the copper surface. The lack of any translational and rotational cooling is discussed within the framework of a model. Faisant appel i la spectroscopie de fluorescence induite au laser, on a CtudiC la rCaction de gravure B sec de surface solides de cuivre par des atomes ou des molCcules de fluor. Le monofluomre de cuivre, CuF, produit par la reaction se forme dans 1'Ctat Clectronique fondamental X'C+ et il se dCsorbe vers la phase gazeuse B des temperatures de surface suptrieures B environ 750 K. Les spectres d'excitation LIF, rCsolus en fonction de la rotation, du systkme de bandes C ' n + X'C+ des molCcules de CuF qui se dCsorbent d'un Cchantillon polycristallin de 6 3 C~ isotopiquement purifiC, ont Ct C obtenus dans des conditions de saturation cohtrente. En se basant sur une analyse de 1'Ctat du produit, on en dCduit que les populations de produit rovibrationnel sont en Cquilibre thermique avec la surface. I1 en est de m&me pour la distribution de la vitesse de translation obtenue par des mesures de diplacement Doppler. On peut attribuer un effet important de polarisation, particulikrement fort pour les transitions des branches Q, B une photosClection des niveaux de paritC unique dans les doublets A de 1'Ctat C l n .Une analyse thCorique de la distribution des niveaux J , basCe sur le formalisme de Greene et Zare, montre que le degrC de polarisation mesurC est en bon accord quantitatif avec une distribution isotrope des vecteurs des moments de rotation angulaire. L'Cquilibre vibrationnel et tr...

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Section: Discussionmentioning

confidence: 99%

Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

Bracker¹,

Jakob²,

Näher³

et al. 1994

Can. J. Chem.

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“…17,18,24 Invoking detailed balance, relative reaction probabilities can be obtained from associative desorption experiments. 12,22,23 Using state-selective detection in combination with time-of-flight techniques, such experiments 12 can now determine energy-resolved relative reaction probabilities which are initial-state selected with respect to both the vibrational state (v) and rotational level ( j). Associative desorption experiments can also determine the influence on reaction of the molecule's alignment with respect to the surface by measuring the rotational quadrupole alignment A 0 (2) (v, j) of the angular momentum of the desorbing molecules.…”

Section: Introductionmentioning

confidence: 99%

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

Somers

McCormack

Kroes

et al. 2002

The Journal of Chemical Physics

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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.

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“…While associative desorption 13 and molecular beam 14 experiments have been undertaken for H 2 ϩCu͑100͒, no study of rotational effects has yet been published. The most complete analysis of the existing experiments was performed by Michelsen and Auerbach; 15 by constructing a vibrational state dependent model, they were able to reconcile data from the two separate experiments ͑associative desorption 13 and molecular beam 14 ͒ to produce a single consistent set of results. Unfortunately, whilst these findings offer insight into vibrational effects, rotation was not considered in the model ͑nor could it be, given the available data͒.…”

Section: Introductionmentioning

confidence: 99%

Dissociative adsorption of H2 on Cu(100): Fixed-site calculations for impact at hollow and top sites

Mowrey

Kroes

Baerends

1998

The Journal of Chemical Physics

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We present results of six-dimensional ͑6D͒ quantum wave-packet calculations for the dissociative adsorption of (ϭ0,jϭ4,m j ) H 2 on Cu͑100͒. The potential-energy surface is a fit to points calculated using density-functional theory ͑DFT͒, with the generalized gradient approximation ͑GGA͒, and a slab representation for the surface. New aspects of the methodology we use to adapt the wave function to the symmetry of the surface, which relate to calculations for initial rotational states with odd m j ͑the magnetic quantum number͒, are explained. Invoking detailed balance, we calculate the quadrupole alignment for H 2 as it would be measured in an associative desorption experiment. The reaction of the helicopter (ϭ0,jϭ4,m j ϭ4) state is preferred over that of the (ϭ0,jϭ4,m j ϭ0) cartwheel state for all but the lowest collision energies considered here. The energy dependence of the quadrupole alignment that we predict for (ϭ0,jϭ4) H 2 desorbing from Cu͑100͒ is in good qualitative agreement with velocity-resolved associative desorption experiments for D 2 ϩCu͑111͒. The vibrational excitation probability P(ϭ0,j→ϭ1) is much larger for j ϭ4 than for jϭ0, and the m j -dependence of P(ϭ0,jϭ4,m j →ϭ1) is markedly different from that of the initial-state-resolved reaction probability. For all but the highest collision energies, vibrational excitation from the (ϭ0,jϭ4) state is accompanied by loss of rotational energy, in agreement with results of molecular beam experiments on scattering of H 2 and D 2 from Cu͑111͒.

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The purely “fast” distribution of H2 and D2 molecules desorbing from Cu(100) and Cu(111) surfaces

Cited by 217 publications

References 14 publications

Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

Internal, translational, and angular momentum product state distributions of CuF molecules desorbing associatively from copper surfaces

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

Dissociative adsorption of H2 on Cu(100): Fixed-site calculations for impact at hollow and top sites

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