School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
J Chem Phys. 2013 Aug 14;139(6):064304. doi: 10.1063/1.4817324.
We present new evidence for the existence of a near threshold π* shape resonance as a common feature in the photoionization of each isomer of difluorobenzene. Experimentally, this is revealed by significant changes in the anisotropy of the photoelectron angular distributions (PADs) following the ionization of the optically aligned S1 state of these molecules at varying photon energies. Continuum multiple scattering Xα calculations reproduce this behaviour well, and allow the visualisation of the continuum shape resonances. The resonances are unusually narrow in energy (<1 eV), but nevertheless appear to extend right down to the ionization thresholds--exactly the low energy range typically accessed in laser-based resonance enhanced multiphoton ionization (REMPI) schemes. The anticipation of such pronounced energy dependence in the PADs and cross-sections sought for other molecules, and an ability to accurately predict such features, should be important for the reliable application and interpretation of experiments involving REMPI probing of those molecules.
我们提出了新的证据，证明在二氟苯的每个异构体的光电离中，存在一个近阈π*形状共振，这是一个共同的特征。实验上，这是通过在不同的光子能量下，这些分子的光对准 S1 态的光电离后，光电子角分布（PAD）的各向异性发生显著变化而揭示的。连续态多散射 Xα 计算很好地再现了这种行为，并允许可视化连续形状共振。这些共振的能量非常窄（<1 eV），但似乎一直延伸到电离阈值——正好是激光基共振增强多光子电离（REMPI）方案通常达到的低能范围。在寻找其他分子的 PAD 和截面中预期会有如此明显的能量依赖性，以及能够准确预测这些特征的能力，对于涉及 REMPI 探测这些分子的实验的可靠应用和解释应该是重要的。
