Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India.
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Chem Phys. 2017 Feb 21;146(7):074705. doi: 10.1063/1.4976133.
A comparative study of mode-selectivity of water dissociation on Ni(100), Ni(110), and Ni(111) surfaces is performed at the same level of theory using a fully quantum approach based on the reaction path Hamiltonian. Calculations show that the barrier to water dissociation on the Ni(110) surface is significantly lower compared to its close-packed counterparts. Transition states for this reaction on all three surfaces involve the elongation of one of the O-H bonds. A significant decrease in the symmetric stretching and bending mode frequencies near the transition state is observed in all three cases and in the vibrational adiabatic approximation, excitation of these softened modes results in a significant enhancement in reactivity. Inclusion of non-adiabatic couplings between modes results in the asymmetric stretching mode showing a similar enhancement of reactivity as the symmetric stretching mode. Dissociation probabilities calculated at a surface temperature of 300 K showed higher reactivity at lower collision energies compared to that of the static surface case, underlining the importance of lattice motion in enhancing reactivity. Mode selective behavior is similar on all the surfaces. Molecules with one-quantum of vibrational excitation in the symmetric stretch, at lower energies (up to ∼0.45 eV), are more reactive on Ni(110) than the Ni(100) and Ni(111) surfaces. However, the dissociation probabilities approach saturation on all the surfaces at higher incident energy values. Overall, Ni(110) is found to be highly reactive toward water dissociation among the low-index nickel surfaces owing to a low reaction barrier resulting from the openness and corrugation of the surface. These results show that the mode-selective behavior does not vary with different crystal facets of Ni qualitatively, but there is a significant quantitative effect.
采用基于反应路径哈密顿量的完全量子方法，在相同理论水平上对 Ni(100)、Ni(110)和 Ni(111)表面上水离解的模式选择性进行了比较研究。计算表明，与密排表面相比，Ni(110)表面上水离解的势垒显著降低。该反应在所有三个表面上的过渡态都涉及到一个 O-H 键的伸长。在所有三种情况下，在过渡态附近都观察到对称伸缩和弯曲模式频率的显著降低，并且在振动绝热近似中，这些软化模式的激发会导致反应性显著增强。包括模式之间的非绝热耦合会导致对称伸缩模式的反应性与对称伸缩模式相似地增强。在表面温度为 300 K 的情况下计算的离解概率表明，与静态表面情况相比，在较低的碰撞能下，反应性更高，这强调了晶格运动在增强反应性方面的重要性。在所有表面上，模式选择性行为是相似的。在较低的能量（高达约 0.45 eV）下，具有一个量子振动激发的对称伸缩分子在 Ni(110)上比 Ni(100)和 Ni(111)表面更具反应性。然而，在更高的入射能值下，所有表面上的离解概率都趋于饱和。总的来说，由于表面的开放性和波纹状，Ni(110)表面对水离解具有很高的反应性，这是由于反应势垒较低所致。这些结果表明，模式选择性行为在不同的 Ni 晶面之间没有定性的变化，但存在显著的定量影响。
