Mehler A, Néel N, Bocquet M-L, Kröger J
Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany.
J Phys Condens Matter. 2019 Feb 13;31(6):065001. doi: 10.1088/1361-648X/aaf54c. Epub 2018 Nov 30.
Vibronic excitations in molecules are key to the fundamental understanding of the interaction between vibrational and electronic degrees of freedom. In order to probe the genuine vibronic properties of a molecule even after its adsorption on a surface appropriate buffer layers are of paramount importance. Here, vibrational progression in both molecular frontier orbitals is observed with submolecular resolution on a graphene-covered metal surface using scanning tunnelling spectroscopy. Accompanying calculations demonstrate that the vibrational modes that cause the orbital replica in the progression share the same symmetry as the electronic states they couple to. In addition, the vibrational progression is more pronounced for separated molecules than for molecules embedded in molecular assemblies. The entire vibronic spectra of these molecular species are moreover rigidly shifted with respect to each other. This work unravels intramolecular changes in the vibronic and electronic structure owing to the efficient reduction of the molecule-metal hybridization by graphene.
分子中的振动电子激发对于深入理解振动自由度与电子自由度之间的相互作用至关重要。为了探究分子即使在吸附于表面后仍具有的真实振动电子特性，合适的缓冲层至关重要。在此，利用扫描隧道光谱在覆盖石墨烯的金属表面以亚分子分辨率观测到了分子前沿轨道中的振动进程。伴随的计算表明，在该进程中导致轨道复制的振动模式与它们所耦合的电子态具有相同的对称性。此外，分离分子的振动进程比嵌入分子聚集体中的分子更为明显。而且，这些分子种类的整个振动电子光谱彼此之间发生了刚性位移。这项工作揭示了由于石墨烯有效降低了分子 - 金属杂化作用而导致的分子内振动电子结构和电子结构的变化。
