Sinha Shreya, Saalfrank Peter
Theoretical Chemistry, Institute of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany.
Phys Chem Chem Phys. 2021 Apr 7;23(13):7860-7874. doi: 10.1039/d0cp05198e. Epub 2020 Nov 27.
Somewhat surprisingly, inverted ("O-down") CO adsorbates on NaCl(100) were recently observed experimentally after infrared vibrational excitation (Lau et al., Science, 2020, 367, 175-178). Here we characterize these species using periodic density functional theory and a quantum mechanical description of vibrations. We determine stationary points and minimum energy paths for CO inversion, for low (1/8 and 1/4 monolayers (ML)) and high (1 ML) coverages. Transition state theory is applied to estimate thermal rates for "C-down" to "O-down" isomerization and the reverse process. For the 1/4 ML p(1 × 1) structure, two-dimensional and three-dimensional potential energy surfaces and corresponding anharmonic vibrational eigenstates obtained from the time-independent nuclear Schrödinger equation are presented. We find (i) rather coverage-independent CO inversion energies (of about 0.08 eV or 8 kJ mol per CO) and corresponding classical activation energies for "C-down" to "O-down" isomerization (of about 0.15 eV or 14 kJ mol per CO); (ii) thermal isomerization rates at 22 K which are vanishingly small for the "C-down" to "O-down" isomerization but non-negligible for the back reaction; (iii) several "accidentally degenerate" pairs of eigenstates well below the barrier, each pair describing "C-down" to "O-down" localized states.
有点令人惊讶的是，最近在红外振动激发后，实验观察到氯化钠（100）表面存在倒置的（“O向下”）一氧化碳吸附物（Lau等人，《科学》，2020年，367卷，175 - 178页）。在此，我们使用周期性密度泛函理论和振动的量子力学描述对这些物种进行表征。我们确定了低覆盖度（1/8和1/4单层（ML））和高覆盖度（1 ML）下一氧化碳反转的驻点和最小能量路径。应用过渡态理论来估计“C向下”到“O向下”异构化及其逆过程的热速率。对于1/4 ML p(1×1)结构，给出了二维和三维势能面以及从与时间无关的核薛定谔方程得到的相应非谐振动本征态。我们发现：（i）一氧化碳反转能量（每个一氧化碳约为0.08电子伏特或8千焦每摩尔）和“C向下”到“O向下”异构化的相应经典活化能（每个一氧化碳约为0.15电子伏特或14千焦每摩尔）与覆盖度关系不大；（ii）在22 K时，“C向下”到“O向下”异构化的热异构化速率极小，但逆反应的速率不可忽略；（iii）有几对在势垒以下“意外简并”的本征态，每一对描述“C向下”到“O向下”的局域态。
