Diffuse Unoccupied Molecular Orbital of Rubrene Causing Image-Potential State Mediated Excitation
Diffuse Unoccupied Molecular Orbital of Rubrene Causing Image-Potential State Mediated Excitation
复制标题
红荧烯的弥漫未占据分子轨道引起图像势态介导的激发
DOI：
10.1021/jp407933m
复制
发表时间：
2013
影响因子：
3.7
通讯作者：
T. Munakata
中科院分区：
文献类型：
--
作者：
T Ueba;R. Terawaki;T. Morikawa;Y. Kitagawa;M Okumura. T. Yamada;H S. Kato;T. Munakata
我们显示了在红荧烯/石墨界面的光激发过程中的里德堡样未占分子轨道的重要作用。双光子光电发射（2 PPE）光谱揭示了在费米能级以上3.26 eV处的未占据分子轨道（MO）的显著强的共振激发（J. Phys.Chem.C2012，116，5821）。激发归因于介导的石墨上的图像电位状态（IPS）。本文通过2 PPE光谱和密度泛函理论（DFT）计算研究了分子轨道的性质。涉及扩散原子轨道的DFT计算预测了在感兴趣的能量下，在四个苯环上延伸的近圆柱形未占据MO。2 PPE光谱的偏振依赖性表明，根据计算的MO，未占据的MO几乎对称于光入射平面。IPS的二维自由电子波函数可以与分子框架内没有节点的MO相互作用。扩散原子轨道的成键相互作用是圆柱MO的起源。它可以被看作是类里德伯轨道，类似于C60的超原子分子轨道（SAMO）。
We show the significant role of the Rydberg-like unoccupied molecular orbital in the photoexcitation process at the rubrene/graphite interface. Two-photon photoemission (2PPE) spectroscopy revealed a prominently strong resonant excitation of an unoccupied molecular orbital (MO) at 3.26 eV above the Fermi level (J. Phys. Chem. C2012,116, 5821). The excitation was attributed to be mediated by the image potential state (IPS) on graphite. We investigate in this paper the nature of the MO by 2PPE spectroscopy and density functional theory (DFT) calculations. The DFT calculation involving diffuse atomic orbitals predicts a nearly cylindrical unoccupied MO extending over four phenyl rings at the energy of the interest. Polarization dependence of 2PPE spectroscopy shows that the unoccupied MO is nearly symmetric to the plane of the light incidence in accordance with the calculated MO. The two-dimensional free electron wave function of the IPS can interact with the MO that has no node within the molecular framework. The bonding interactions of diffuse atomic orbitals are the origin of the cylindrical MO. It can be seen as a Rydberg-like orbital and is similar to the superatom molecular orbital (SAMO) known for C60.