Spatially Resolved Vibronic Excitations of an Isolated Adsorbed Organometallic Complex via Multiple Tunneling Channels

Vibronic excitations of molecules at nanoscale interfaces are important for molecular electronics and spintronics and have therefore attracted considerable attention. For single molecules in mechanically controlled break junctions or in a scanning tunneling microscope (STM), vibronic excitations are typically described by a double-barrier tunneling junction model. In this model, a homogeneous electric field is considered and the atomic structure of the metal contacts is neglected. Here, we report experimental STM data of a new nonplanar organometallic complex, [Mo(CO)_{3}(Pyridine_{3}S_{3})], on Ag(111). Spatially resolved maps of the vibronic excitations show several features related to the reordering of the occupied molecular orbitals due to the rapidly decaying potential of the tip apex. Such rearrangement leads to a significant shift in the vibronic levels as the tip position is changed. These observations, together with our modelling results, demonstrate that the molecular orbitals can be controlled by the field of the STM tip, whose atomic-scale variation deserves more attention in studies of nonplanar molecules.