Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0299, USA.
J Chem Phys. 2012 Feb 7;136(5):054309. doi: 10.1063/1.3682541.
We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C-H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions. The pulses (50 fs, 800 nm) are focused into the molecular vapor, and ion mass spectra are recorded for intensities of ~10(13) W/cm(2) to ~10(15) W/cm(2). We measure ion yields in the absence of the focal volume effect without the need for deconvolution of the data. For all targets, stable singly- and doubly-charged parent ions (C(6-n)H(6-n)N(n)(+(+))) are observed with features suggesting resonance-enhanced ionization. From the intensity dependence of the ion yield, we infer that excitation occurs both through (1)ππ* transitions (remnants of the benzene structure) and through (1)nπ* transitions, the latter being a result of Rydberg-like excitations of the lone pair electrons of the nitrogen atoms. Stability against intense-field fragmentation is also discussed.
我们报告了吡啶、哒嗪、嘧啶和吡嗪的超快光致电离。这四个分子代表了苯环结构的一系列系统扰动，探索了用氮原子取代 C-H 实体，形成杂环结构。数据是在强场、单分子条件下记录的。脉冲（50fs，800nm）聚焦到分子蒸气中，并记录了约 10(13)W/cm(2)至 10(15)W/cm(2)强度的离子质谱。我们在没有需要对数据进行反卷积的焦点体积效应的情况下，在不存在焦点体积效应的情况下测量离子产率。对于所有的靶标，都观察到稳定的单电荷和双电荷母体离子（C(6-n)H(6-n)N(n)(+(+)))，其特征表明存在共振增强电离。从离子产率的强度依赖性推断，激发既通过（1）ππ跃迁（苯结构的残留物）发生，也通过（1）nπ跃迁发生，后者是氮原子孤对电子的类 Rydberg 激发的结果。还讨论了对强场碎裂的稳定性。
