Department of Chemistry and Cherry Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, United States.
J Phys Chem A. 2023 Mar 2;127(8):1975-1987. doi: 10.1021/acs.jpca.2c05844. Epub 2023 Feb 17.
We develop a multireference quantum embedding model to investigate a recent experimental observation of the isomerization of vibrationally excited CO molecules on a NaCl(100) surface [ , , 175-178]. To explore this mechanism, we built a reduced potential energy surface of CO interacting with NaCl(100) using a second-order multireference perturbation theory, modeling the adsorbate-surface interaction with our previously developed active space embedding theory (ASET). We considered an isolated CO molecule on NaCl(100) and a high-coverage CO monolayer (1/1), and for both we generated potential energy surfaces parametrized by the CO stretching, adsorption, and inversion coordinates. These surfaces are used to determine stationary points and adsorption energies and to perform a vibrational analysis of the states relevant to the inversion mechanism. We found that for near-equilibrium bond lengths, CO adsorbed in the C-down configuration is lower in energy than in the O-down configuration. Stretching of the C-O bond reverses the energetic order of these configurations, supporting the accepted isomerization mechanism. The vibrational constants obtained from these potential energy surfaces show a small (< 10 cm) blue- and red-shift for the C-down and O-down configurations, respectively, in agreement with experimental assignments and previous theoretical studies. Our vibrational analysis of the monolayer case suggests that the O-down configuration is energetically more stable than the C-down one beyond the 16th vibrational excited state of CO, a value slightly smaller than the one from quasi-classical trajectory simulations (22nd) and consistent with the experiment. Our analysis suggests that CO-CO interactions in the monolayer play an important role in stabilizing highly vibrationally excited states in the O-down configuration and reducing the barrier between the C-down and O-down geometries, therefore playing a crucial role in the inversion mechanism.
我们开发了一种多参考量子嵌入模型，以研究最近关于在 NaCl(100)表面振动激发的 CO 分子异构化的实验观察[,, 175-178]。为了探索这种机制，我们使用二阶多参考微扰理论构建了 CO 与 NaCl(100)相互作用的简化势能面，并用我们之前开发的活性空间嵌入理论 (ASET) 来模拟吸附剂-表面相互作用。我们考虑了孤立的 CO 分子在 NaCl(100)上和高覆盖度的 CO 单层（1/1）上的情况，对于这两种情况，我们生成了由 CO 拉伸、吸附和反转坐标参数化的势能面。这些表面用于确定稳定点和吸附能，并对与反转机制相关的态进行振动分析。我们发现，对于接近平衡的键长，C 向下构型吸附的 CO 能量低于 O 向下构型。C-O 键的拉伸扭转了这些构型的能量顺序，支持了公认的异构化机制。从这些势能面得到的振动常数显示 C 向下和 O 向下构型的蓝移和红移分别小于 10 cm，与实验分配和以前的理论研究一致。我们对单层情况的振动分析表明，在 CO 的第 16 个振动激发态之后，O 向下构型比 C 向下构型在能量上更稳定，这一值略小于准经典轨迹模拟（第 22 个）的值，与实验值一致。我们的分析表明，在单层中 CO-CO 相互作用在稳定 O 向下构型的高振动激发态和降低 C 向下和 O 向下构型之间的势垒方面起着重要作用，因此在反转机制中起着至关重要的作用。
