Diffractive and reactive scattering of (v=0, j=0) HD from Pt(111): Six-dimensional quantum dynamics compared with experiment

Abstract

We present results of (vϭ0, jϭ0) HD reacting on and scattering from Pt͑111͒ at off-normal angles of incidence, treating all six molecular degrees of freedom quantum mechanically. The six-dimensional potential energy surface ͑PES͒ used was obtained from density functional theory, using the generalized gradient approximation and a slab representation of the metal surface. Diffraction and rotational excitation probabilities are compared with experiment for two incidence directions, at normal incidence energies between 0.05-0.16 eV and at a parallel translational energy of 55.5 meV. The computed ratio of specular reflection to nonspecular in-plane diffraction for HDϩPt͑111͒ is lower than found experimentally, and lower for HDϩPt͑111͒ than for H 2 ϩPt(111) for both incidence directions studied. The calculations also show that out-of-plane diffraction is much more efficient than in-plane diffraction, underlining that results from experiments that solely attempt to measure in-plane diffraction are not sufficient to show the absence of surface corrugation. Discrepancies in rotational excitation and diffraction probabilities between theory and experiment are discussed, as well as possible future improvements in the dynamical model and in the calculation of the PES.

Comparative dynamical study of the HD and isotopomers interacting with Pd(111) and Cu(110) surfaces

“…These factors decrease when E i increases simply because of the decrease of N ref ðJ f ¼ 0Þ for both molecules. A larger fraction of rotationally excited HD molecules compared to the case of H 2 has been also observed in Q results for H 2 and HD interacting with Pt(1 1 1) [2]. However, in the latter case, the difference between both molecules is larger than in the present case.…”

“…In the latter case, this difference was attributed to a competition between the adsorption and rotational excitation channels for HD stronger than for H 2 , because above the dissociation threshold (i.e. $50 meV) the rotational excitation probability, P rotexc , of HD molecules is much larger than for H 2 [2]. In contrast, for Cu(1 1 0), above the dissociation threshold ($400 meV) the rotational excitation probabilities of H 2 [28] and HD molecules are both large (see the inset of Fig.…”

“…The lower dissociative adsorption probability for HD was attributed to a stronger competition with rotational excitation channels whereas the higher rotational excitation probabilities were attributed to the following factors [2]: (i) for a given initial impact energy, there exist more open rotational excitation channels for HD than for H 2 because rotational transitions with both even and odd values of DJ ¼ J f À J i (the change of the rotational quantum number, J) are allowed for HD and a larger moment of inertia decreases the energy gaps between rotational states; (ii) for HD the molecular center of mass is displaced with respect to the molecular center of charge which increases the effective angular corrugation of the PES (for a fixed position of the molecular center of mass) which favors rotational excitation.…”

“…Most of them have considered the homonuclear isotopomer H 2 (and in less extent also D 2 ). In one of the very few theoretical investigations for the heteronuclear isotopomer HD, Kingma et al [2] presented a comparison of dissociative adsorption and rotational excitation probabilities of HD and H 2 molecules interacting with Pt(1 1 1) obtained in quantum dynamical calculations. For HD molecules, they reported slightly smaller dissociative adsorption probabilities and much larger total rotational excitation probabilities than for H 2 .…”

The plane wave packet approach to quantum scattering theory

“…Nevertheless, it is worth bearing in mind that the PWP approach can be used with time-independent methods, if only to clarify that the PWP approach is a method of interpretation, rather than a numerical method of solving the Schro¨dinger equation. Regarding the latter, there are a variety of excellent methods in the literature [22][23][24][25][26][27][28][29], which could be adapted to implement efficiently the PWP approach.…”