Novotný O, Sivaraman B, Rebrion-Rowe C, Travers D, Biennier L, Mitchell J B A, Rowe B R
Laboratoire de Physique des Atomes, Lasers, Molécules et Surfaces (PALMS), Unite Mixte de Recherché (UMR), No. 6627 du Centre National de la Recherché Scientifique (CNRS), Université de Rennes I, France.
J Chem Phys. 2005 Sep 8;123(10):104303. doi: 10.1063/1.2000927.
A new technique, flowing afterglow with photoions (FIAPI), has been developed to measure the rate coefficient for the recombination of complex ions, and, in particular, polycyclic aromatic hydrocarbon (PAH) cations with electrons. The method is based on the flowing afterglow Langmuir probe - mass spectrometer apparatus at the University of Rennes I. A helium plasma is generated by a microwave discharge in a He buffer gas and downstream, a small amount of argon gas is injected to destroy any helium metastables. A very small amount of neutral PAH molecules is added to the afterglow plasma by evaporation from a plate coated with the PAH to be studied. PAH ions are then produced by photoionization of the parent molecule using a pulsed UV laser (157 nm). The laser beam is oriented along the flow tube and so a constant spatial concentration of photoions is obtained. The electron concentration along the flow tube is measured by means of a movable Langmuir probe. Ion concentration decay in time is measured at a fixed position using a quadrupole mass spectrometer which is triggered by the laser pulse. The recombination of anthracene and pyrene cations has been studied using this technique and we have found a recombination rate of (2.4 +/- 0.8) x 10(-6) cm(3) s(-1) for anthracene and (4.1 +/- 1.2) x 10(-6) cm(3) s(-1) for pyrene.
一种新的技术——光离子流动余辉（FIAPI）已被开发出来，用于测量复合离子，特别是多环芳烃（PAH）阳离子与电子复合的速率系数。该方法基于雷恩第一大学的流动余辉朗缪尔探针 - 质谱仪装置。在氦缓冲气体中通过微波放电产生氦等离子体，在下游注入少量氩气以消除任何氦亚稳态。通过从涂有待研究PAH的平板蒸发，将极少量的中性PAH分子添加到余辉等离子体中。然后使用脉冲紫外激光（157nm）对母体分子进行光电离产生PAH离子。激光束沿流管方向定向，因此获得了光离子的恒定空间浓度。通过可移动的朗缪尔探针测量沿流管的电子浓度。使用四极质谱仪在固定位置测量离子浓度随时间的衰减，该质谱仪由激光脉冲触发。使用该技术研究了蒽和芘阳离子的复合，我们发现蒽的复合速率为(2.4±0.8)×10⁻⁶cm³ s⁻¹，芘的复合速率为(4.1±1.2)×10⁻⁶cm³ s⁻¹。
