Khatymov Rustem V, Muftakhov Mars V, Shchukin Pavel V
Institute of Molecule and Crystal Physics, Ufa Research Center of Russian Academy of Sciences, IМСР URC RAS, Prospekt Oktyabrya 151, Ufa, 450075, Russia.
Rapid Commun Mass Spectrom. 2017 Oct 30;31(20):1729-1741. doi: 10.1002/rcm.7945.
Polycyclic aromatic hydrocarbons are molecules of ecological, astrochemical significance that find practical applications in organic electronics, photonics and the chemical synthesis of novel materials. The utility of these molecules often implies the occurrence of their ionized forms. Studies in the gas phase of elementary processes of energy-controlled interaction of molecules with low-energy electrons shed light on the mechanisms of transient negative ion formation and evolution.
Experiments with the individual compounds representing homologous and/or isomeric series of cata-condensed polyaromatic hydrocarbons were carried out by means of negative ion mass spectrometry in the resonant electron capture mode. Literature data obtained by complementary techniques and theoretical quantum chemical methods (ab initio and density functional theory (DFT)) were invoked to treat the experimental observations.
Most polycyclic aromatic hydrocarbon (PAH) molecules form long-lived molecular negative ions when exposed to free electrons of thermal or epi-thermal energy, and no fragmentation is observed up to ca 5 eV. The lifetimes of such ions with respect to the spontaneous loss of extra-electron vary from tens of microseconds for angular and branched PAH molecules to milliseconds for linear ones, and correlate with the adiabatic electron affinity (EA) of molecules. Detailed analysis of the electronic (orbital) structure of the molecules made it possible to rationalize the relatively low EAs of angular and branched PAH compared with those of linear ones.
The obtained results contribute to the field of electron-molecule interactions and may be of importance for the better comprehension of the functioning of organic electronics, for the synthesis of relevant novel materials, and the development of efficient analytical methods capable of discriminating structural isomers.
多环芳烃是具有生态和天体化学意义的分子，在有机电子学、光子学和新型材料的化学合成中有实际应用。这些分子的效用通常意味着其离子化形式的存在。对分子与低能电子的能量控制相互作用的基本过程进行的气相研究揭示了瞬态负离子形成和演化的机制。
通过负离子质谱在共振电子捕获模式下对代表并缩合多环芳烃的同源和/或异构系列的单个化合物进行实验。调用通过互补技术和理论量子化学方法（从头算和密度泛函理论（DFT））获得的文献数据来处理实验观察结果。
大多数多环芳烃（PAH）分子在暴露于热能或超热能的自由电子时会形成长寿命的分子负离子，并且在高达约5 eV的能量下未观察到碎片化。这种离子相对于额外电子自发损失的寿命从角形和支链PAH分子的几十微秒到线性分子的毫秒不等，并且与分子的绝热电子亲和力（EA）相关。对分子的电子（轨道）结构进行详细分析，使得能够解释角形和支链PAH与线性PAH相比相对较低的EA。
所获得的结果有助于电子 - 分子相互作用领域，对于更好地理解有机电子学的功能、合成相关新型材料以及开发能够区分结构异构体的高效分析方法可能具有重要意义。
