Institut des Sciences Moléculaires d'Orsay (UMR 8214 Université Paris-Sud et CNRS), Bat. 210-350, Université Paris Sud, F-91405 Orsay Cedex, France.
J Chem Phys. 2013 Jul 28;139(4):044311. doi: 10.1063/1.4811713.
We report a combined experimental and theoretical study of photoionization (PI) of the NO2 molecule into the NO2(+) (X (1)Σg(+)) ground state and the photodissociation of NO2 into the NO(+)((1)Σ(+)) + O(-)((2)P) ion pair. These processes were induced by 10.9 eV-13 eV synchrotron radiation and the products were detected using electron-ion or O(-)-NO(+) coincident momentum spectroscopy. The results demonstrate the strong influence of [R(∗)(4b2)(-1), nlα(i), v2(')] Rydberg states vibrationally resolved in the v2(') bending modes for both processes. In particular, we emphasize two regions around 11.5 eV and 12.5 eV that were studied in more detail for their relevance to 400 nm multiphoton ionization induced by femtosecond pulses. The photoelectron energy spectra and asymmetry parameters support the existence of two PI mechanisms, as probed with the help of fixed-nuclei frozen-core Hartree-Fock calculations. We found significant deviations from Franck-Condon ionization predictions which may be assigned to vibronic coupling of NO2(∗) states such as that induced by a conical intersection. The limited agreement between theory and experiment, even for the non-resonant processes, indicates the need for calculations that go beyond the approximations used in the current study. Ion pair formation leads to strong vibrational and rotational excitation of the NO(+)((1)Σ(+),v) product, with an ion fragment angular anisotropy depending on both the v2(') bending quantum number of the excited parent molecule and the v vibrational level of the fragment.
我们报告了一项关于二氧化氮分子光解为基态二氧化氮正离子（X ¹Σg⁺）和一氧化氮离子（¹Σ⁺）+氧负离子（²P）离子对的实验和理论研究。这些过程是由 10.9 eV-13 eV 的同步辐射诱导的，产物通过电子-离子或氧负离子-一氧化氮离子对的动量谱学检测。结果表明，在两个过程中，[R(∗)(4b2)(-1), nlα(i), v2(')] Rydberg 态在 v2(') 弯曲模式下的振动分辨率对过程有强烈的影响。特别是，我们强调了在 11.5 eV 和 12.5 eV 周围的两个区域，因为它们与飞秒脉冲诱导的 400nm 多光子电离有关。光电电子能谱和不对称参数支持两种光电离机制的存在，这是通过固定核哈特里-福克计算得到的。我们发现了与 Franck-Condon 电离预测的显著偏差，这可能归因于 NO2(∗)态的振动态耦合，例如由锥形交叉诱导的耦合。即使对于非共振过程，理论与实验之间的有限一致性也表明需要进行超出当前研究中使用的近似的计算。离子对的形成导致了 NO(+)（¹Σ⁺，v）产物的强烈的振动和转动激发，离子碎片的角各向异性取决于激发母体分子的 v2(') 弯曲量子数和碎片的 v 振动能级。
