PDF(Pubmed)
Abstract：
Vibrational quanta of melamine and its tautomer are analyzed at the single-molecule level on Cu(100) with inelastic electron tunneling spectroscopy. The on-surface tautomerization gives rise to markedly different low-energy vibrational spectra of the isomers, as evidenced by a shift in mode energies and a variation in inelastic cross sections. Spatially resolved spectroscopy reveals the maximum signal strength on an orbital nodal plane, excluding resonant inelastic tunneling as the mechanism underlying the quantum excitations. Decreasing the probe-molecule separation down to the formation of a chemical bond between the melamine amino group and the Cu apex atom of the tip leads to a quenched vibrational spectrum with different excitation energies. Density functional and electron transport calculations reproduce the experimental findings and show that the shift in the quantum energies applies to internal molecular bending modes. The simulations moreover suggest that the bond formation represents an efficient manner of tautomerizing the molecule.
摘要：
使用非弹性电子隧道光谱法在Cu（100）上的单分子水平上分析了三聚氰胺及其互变异构体的振动量子。表面互变异构化导致异构体的低能振动光谱明显不同，模式能量的变化和非弹性横截面的变化证明了这一点。空间分辨光谱学揭示了轨道节点平面上的最大信号强度，排除共振非弹性隧穿作为量子激发的潜在机制。将探针-分子分离降低到三聚氰胺氨基与尖端的Cu顶点原子之间形成化学键，会导致具有不同激发能量的猝灭振动光谱。密度泛函和电子传输计算再现了实验结果，并表明量子能量的偏移适用于内部分子弯曲模式。此外，模拟表明，键的形成代表了分子互变异构的有效方式。
