Vibrational Excitation of H₂ Scattering from Cu(111): Effects of Surface Temperature and of Allowing Energy Exchange with the Surface

Abstract

In scattering of H2 from Cu(111), vibrational excitation has so far defied an accurate theoretical description. To expose the causes of the large discrepancies with experiment, we investigate how the feature due to vibrational excitation (the “gain peak”) in the simulated time-of-flight spectrum of (v = 1, j = 3) H2 scattering from Cu(111) depends on the surface temperature (Ts) and the possibility of energy exchange with surface phonons and electron–hole pairs (ehp’s). Quasi-classical dynamics calculations are performed on the basis of accurate semiempirical density functionals for the interaction with H2 + Cu(111). The methods used include the quasi-classical trajectory method within the Born–Oppenheimer static surface model, the generalized Langevin oscillator (GLO) method incorporating energy transfer to surface phonons, the GLO + friction (GLO+F) method also incorporating energy exchange with ehp’s, and ab initio molecular dynamics with electronic friction (AIMDEF). Of the quasi-classical methods tested, comparison with AIMDEF suggests that the GLO+F method is accurate enough to describe vibrational excitation as measured in the experiments. The GLO+F calculations also suggest that the promoting effect of raising Ts on the measured vibrational excitation is due to an electronically nonadiabatic mechanism. However, by itself, enabling energy exchange with the surface by modeling surface phonons and ehp’s leads to reduced vibrational excitation, further decreasing the agreement with experiment. The simulated gain peak is quite sensitive to energy shifts in calculated vibrational excitation probabilities and to shifts in a specific experimental parameter (the chopper opening time). While the GLO+F calculations allow important qualitative conclusions, comparison to quantum dynamics results suggests that, with the quasi-classical way of describing nuclear motion and the present box quantization method for assigning the final vibrational state, the gain peak is not yet described with quantitative accuracy. Ways in which this problem might be resolved in the future are discussed.

Designing new SRP density functionals including non-local vdW-DF2 correlation for H2 + Cu(111) and their transferability to H2 + Ag(111), Au(111) and Pt(111)

“…We start with the vibrationally inelastic scattering results for H 2 shown in figure 15. We specifically show QD results since the previously voiced expectation that vibrationally inelastic scattering should be well described using the QCT method for translational energies above the lowest barrier to reaction 163 has been shown not to hold 24 . Here we discuss the inelastic scattering probability P(ν = 0, J → ν = 1, J = 3) for three different initial J states.…”

“…Furthermore we will treat vibrationally and rotationally inelastic scattering for the H 2 + Cu (111) system, since the opinion has been voiced that these properties might be extra sensitive to the Van der Waals well, which is present in potential energy surfaces (PESs) computed here with the use of non-local correlation 24 .…”

Dynamics of N2 sticking on W(100): the decisive role of van der Waals interactions

“…Oppenheimer approximation, making use of potential energy surfaces (PES) based on density functional theory (DFT) and the generalized gradient approximation (GGA) for the exchangecorrelation (EXC) functional. Within this level of theory different phenomena including reactivity [18][19][20][21][22][23] and also scattering properties such as diffraction peak positions 18,24 and angular 21,25 , internal state [26][27][28][29] and energy distributions 25,30 of the scattered particles, have been reasonably well described for a variety of molecule-surface combinations.…”

Energy dissipation to tungsten surfaces upon hot-atom and Eley–Rideal recombination of H2

“…12 For instance, in fast processes such as dissociative adsorption or scattering, electronic excitations are in general found to negligibly a , CNRS, ISM, UMR5255, F-33400 Talence affect the probabilities of the processes. [13][14][15][16][17][18][19] In contrast, nonadiabaticity might be crucial in order to describe final energy distributions of light scattered species [20][21][22][23] as well as processes involving hyperthermal diffusion of the gas compound on the surface. [24][25][26][27] The characteristics of the system of interest such as the chemical species involved, 25 the surface coverage, 26 and the surface temperature 28 might also be relevant regarding the effect of electronic excitations.…”

“…[37][38][39][40][41][42][43] Among them, the local density friction approximation (LDFA) 12,13,44 offers a good compromise between accuracy of results and simplicity of implementation. This approach has been used to study the energy dissipation in different processes on metal surfaces such as adsorption, 24,45,46 scattering, 19,23,47,48 dissociation, [13][14][15][16][17] recombination, 22,26,27,49,50 and femtosecond laser induced desorption. [51][52][53][54] Making use of this methodology, we investigate here nonadiabatic effects on both abstraction mechanisms for H 2 recombination on H-covered W(100) and W(110) surfaces.…”