Quantum-state-resolved reactivity of overtone excited CH4 on Ni(111): Comparing experiment and theory

Abstract

Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH 4 on Ni(111). IR-IR double resonance excitation in a molecular beam was used to prepare CH 4 in three different vibrational symmetry components, A 1 , E, and F 2 , of the 2ν 3 antisymmetric stretch overtone vibration as well as in the ν 1 + ν 3 symmetric plus antisymmetric C-H stretch combination band of F 2 symmetry. The quantum state specific dissociation probability S 0 (sticking coefficient) was measured for each of the four vibrational states by detecting chemisorbed carbon on Ni(111) as the product of CH 4 dissociation by Auger electron spectroscopy. We observe strong mode specificity, where S 0 for the most reactive state ν 1 + ν 3 is an order of magnitude higher than for the least reactive, more energetic 2ν 3 -E state. Our first principles quantum scattering calculations show that as molecules in the ν 1 state approach the surface, the vibrational amplitude becomes localized on the reacting C-H bond, making them very reactive. This behavior results from the weakening of the reacting C-H bond as the molecule approaches the surface, decoupling its motion from the three non-reacting C-H stretches. Similarly, we find that overtone normal mode states with more ν 1 character are more reactive: S 0 (2ν 1 ) > S 0 (ν 1 + ν 3 ) > S 0 (2ν 3 ). The 2ν 3 eigenstates excited in the experiment can be written as linear combinations of these normal mode states. The highly reactive 2ν 1 and ν 1 + ν 3 normal modes, being of A 1 and F 2 symmetry, can contribute to the 2ν 3 -A 1 and 2ν 3 -F 2 eigenstates, respectively, boosting their reactivity over the E component, which contains no ν 1 character due to symmetry. Published by AIP Publishing.

Transferability of the SRP32-vdW specific reaction parameter functional to CHD3 dissociation on Pt(110)-(2 × 1)

“…All distributions were calculated using Eq. (5). The solid black line shows the value of θ for the L2 transition state, and the black dashed line shows the value of θ for the K1 transition state.…”

“…1 To be able to describe these reactions theoretically, an accurate method of calculating the activation barrier for the dissociation is required. For gas-surface reactions, generalized gradient approximation (GGA) functionals are usually used within density functional theory [2][3][4][5][6][7][8][9][10] (DFT), although the mean unsigned error of the activation barrier obtained using these functionals is almost 16 kJ/mol even for simpler, gas phase reactions. 11 Whilst this value has not been determined for gas-surface reactions, the activation barriers for dissociation found using typical GGA functionals are not chemically accurate (correct to within 4.2 kJ/mol).…”

“…11 Whilst this value has not been determined for gas-surface reactions, the activation barriers for dissociation found using typical GGA functionals are not chemically accurate (correct to within 4.2 kJ/mol). 12 As a result of the limited accuracy of GGA-DFT, dynamics calculations 2,4,5,[13][14][15][16] based on models of the molecule-surface interaction employing standard GGA functionals such as the Perdew, Burke and Ernzerhof (PBE) functional 17,18 tend to reproduce sticking probabilities of molecules on metals only semi-quantitatively.…”

Mid-Infrared Scattering in γ-Al2O3 Catalytic Powders

“…[1][2][3][4][5][6] Most notably this has been demonstrated for vibrationally excited methane incident on nickel and platinum surfaces. 1,2,7,8 Additionally, there are a number of studies describing the catalysis of thermally activated reactions for molecules under vibrational strong coupling and the associated mechanisms under which the decrease in the activation energy of vibropolaritonic states outcompetes the decrease for that of dark states. [9][10][11] Such research indicates that vibrationally excited molecules may enable catalysis to efficiently occur at lower temperatures, if the challenge of close coupling between excited molecules and the catalyst can be overcome.…”

“…[9][10][11] Such research indicates that vibrationally excited molecules may enable catalysis to efficiently occur at lower temperatures, if the challenge of close coupling between excited molecules and the catalyst can be overcome. [1][2][3][4][5][6][7][8] Thus, a prerequisite for efficient infrared light-assisted catalysis is a detailed understanding of how to efficiently couple light into the catalytic material and distribute it throughout the reactor bed. In this manner, one ensures close overlap of light for excitation and reactant molecules, helping to mitigate the great challenge of short excitation lifetimes.…”