Kersten Hendrik, Funcke Valerie, Lorenz Matthias, Brockmann Klaus J, Benter Thorsten, O'Brien Rob
Department of Physical and Theoretical Chemistry, University of Wuppertal, Wuppertal, Germany.
J Am Soc Mass Spectrom. 2009 Oct;20(10):1868-80. doi: 10.1016/j.jasms.2009.06.014. Epub 2009 Jul 3.
We report on the reactions of neutral radical species [OH, Cl, O(3P), H], generated in a typical atmospheric pressure ionization (API) source upon irradiation of the sample gases with either 193 nm laser radiation or 124 nm VUV light, the latter commonly used in atmospheric pressure photoionization (APPI). The present investigations focus on the polycyclic aromatic hydrocarbon pyrene as representative of the aromatic compound class. Experimental results are supported by computational methods: simple kinetic models are used to estimate the temporal evolution of the concentrations of reactants, intermediates, and final products, whereas density functional theory (DFT) energy calculations are carried out to further elucidate the proposed reaction pathways. The neutral radicals are generated upon photolysis of background water and oxygen always present in appreciable mixing ratios in typical API sources. Substantial amounts of oxygenated analyte product ions are observed using both techniques. In contrast, upon atmospheric pressure laser ionization (APLI) with 248 nm radiation, oxygenated products are virtually absent. In addition, kinetic data evaluation yielded a bimolecular rate constant of k = (1.9 +/- 0.9) x 10(-9) cm3 molecule(-1) s(-1) for the reaction of the pyrene radical cation with OH radicals.
我们报告了在典型的大气压电离（API）源中，当用193 nm激光辐射或124 nm真空紫外光（VUV）照射样品气体时产生的中性自由基物种[OH、Cl、O(³P)、H]的反应，后者常用于大气压光电离（APPI）。本研究聚焦于作为芳香族化合物类代表的多环芳烃芘。实验结果得到了计算方法的支持：使用简单的动力学模型来估计反应物、中间体和最终产物浓度的时间演变，同时进行密度泛函理论（DFT）能量计算以进一步阐明所提出的反应途径。中性自由基是在典型API源中始终以可观混合比存在的背景水和氧气的光解过程中产生的。使用这两种技术均观察到大量的含氧分析物产物离子。相比之下，在使用248 nm辐射的大气压激光电离（APLI）过程中，几乎不存在含氧产物。此外，动力学数据评估得出芘自由基阳离子与OH自由基反应的双分子速率常数为k = (1.9 ± 0.9) x 10⁻⁹ cm³ molecule⁻¹ s⁻¹。
