Abbott H L, Harrison I
Department of Chemistry, University of Virginia, Charlottesville, VA 22904-4319, USA.
J Chem Phys. 2006 Jul 14;125(2):24704. doi: 10.1063/1.2208362.
A simple picture of the hydrogen dissociation/associative desorption dynamics on Cu(111) emerges from a two-parameter, full dimensionality microcanonical unimolecular rate theory (MURT) model of the gas-surface reactivity. Vibrational frequencies for the reactive transition state were taken from density functional theory calculations of a six-dimensional potential energy surface [Hammer et al., Phys. Rev. Lett. 73, 1400 (1994)]. The two remaining parameters required by the MURT were fixed by simulation of experiments. These parameters are the dissociation threshold energy, E(0)=79 kJmol, and the number of surface oscillators involved in the localized H(2)Cu(111) collision complex, s=1. The two-parameter MURT quantitatively predicts much of the varied behavior observed for the H(2) and D(2)Cu(111) reactive systems, including the temperature-dependent associative desorption angular distributions, mean translational energies of the associatively desorbing hydrogen as a function of rovibrational eigenstate, etc. The divergence of the statistical theory's predictions from experimental results at low rotational quantum numbers, J < or approximately 5, suggests that either (i) rotational steering is important to the dissociation dynamics at low J, an effect that washes out at high J, or (ii) molecular rotation is approximately a spectator degree of freedom to the dissociation dynamics for these low J states, the states that dominate the thermal reactivity. Surface vibrations are predicted to provide approximately 30% of the energy required to surmount the activation barrier to H(2) dissociation under thermal equilibrium conditions. The MURT with s=1 is used to analytically confirm the experimental finding that partial differential "E(a)(T(s))" partial differential E(t)= -1 for eigenstate-resolved dissociative sticking at translational energies E(t)<E(0)-E(v)-E(r). Explicit treatment of the surface motion (i.e., surface not frozen at T(s)=0 K) is a relatively novel aspect of the MURT theoretical approach.
通过气体 - 表面反应性的双参数、全维度微正则单分子速率理论（MURT）模型，可以得出氢在Cu(111)表面解离/缔合脱附动力学的简单图像。反应过渡态的振动频率取自六维势能面的密度泛函理论计算[哈默等人，《物理评论快报》73, 1400 (1994)]。MURT所需的另外两个参数通过实验模拟确定。这些参数分别是解离阈值能量E(0)=79 kJ/mol，以及参与局部H₂ - Cu(111)碰撞复合物的表面振子数s = 1。双参数MURT定量预测了H₂和D₂ - Cu(111)反应体系中观察到的许多不同行为，包括与温度相关的缔合脱附角分布、缔合脱附氢的平均平动能随振转本征态的变化等。在低转动量子数J < 或约为5时，统计理论预测与实验结果的偏差表明，要么（i）转动导向对低J时的解离动力学很重要，这种效应在高J时消失；要么（ii）对于这些低J态（主导热反应性的态），分子转动在解离动力学中近似为旁观者自由度。预计在热平衡条件下，表面振动提供跨越H₂解离活化能垒所需能量的约30%。s = 1的MURT用于分析性地确认实验发现：对于平动能E(t)<E(０)-E(v)-E(r)下本征态分辨的解离粘附，∂“E(a)(T(s))”/∂E(t)= -1。明确处理表面运动（即表面在T(s)=0 K时不冻结）是MURT理论方法中一个相对新颖的方面。
