Bellm Susan M, Davies Julia A, Whiteside Paul T, Guo Jingwei, Powis Ivan, Reid Katharine L
School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
J Chem Phys. 2005 Jun 8;122(22):224306. doi: 10.1063/1.1927523.
Previously reported dramatic changes in photoelectron angular distributions (PADs) as a function of photoelectron kinetic energy following the ionization of S1 p-difluorobenzene are shown to be explained by a shape resonance in the b(2g) symmetry continuum. The characteristics of this resonance are clearly demonstrated by a theoretical multiple-scattering treatment of the photoionization dynamics. New experimental data are presented which demonstrate an apparent insensitivity of the PADs to both vibrational motion and prepared molecular alignment, however, the calculations suggest that strong alignment effects may nevertheless be recognized in the detail of the comparison with experimental data. The apparent, but unexpected, indifference to vibrational excitation is rationalized by considering the nature of the resonance. The correlation of this shape resonance in the continuum with a virtual pi* antibonding orbital is considered. Because this orbital is characteristic of the benzene ring, the existence of similar resonances in related substituted benzenes is discussed.
先前报道的，在S1对二氟苯电离后光电子角分布（PADs）随光电子动能的显著变化，被证明是由b(2g)对称连续区中的形状共振所解释。这种共振的特征通过光离化动力学的理论多重散射处理得到了清晰展示。本文给出了新的实验数据，这些数据表明PADs对振动运动和制备的分子取向均表现出明显的不敏感性，然而，计算结果表明，通过与实验数据的详细比较，仍可能识别出强烈的取向效应。通过考虑共振的性质，对这种对振动激发明显但出乎意料的不敏感性进行了合理化解释。本文考虑了连续区中这种形状共振与一个虚拟π*反键轨道的相关性。由于这个轨道是苯环的特征，因此讨论了相关取代苯中类似共振的存在情况。
