de Castilho R B, Ramalho T C, Nunez C V, Coutinho L H, Santos A C F, Pilling S, Lago A F, Silva-Moraes M O, de Souza G G B
Departamento de Química, Instituto de Ciências Exatas, Universidade Federal do Amazonas (UFAM), Campus Universitário, Coroado, 69077-000, Manaus, AM, Brazil.
Rapid Commun Mass Spectrom. 2014 Aug 15;28(15):1769-76. doi: 10.1002/rcm.6961.
An interesting class of volatile compounds, the monoterpenes, is present in some plants although their functions are not yet fully understood. We have studied the interaction of the camphor molecule with monochromatic high-energy photons (synchrotron radiation) using time-of-flight mass spectrometry and coincidence techniques.
A commercial sample of S-camphor was admitted into the vacuum chamber, without purification, through an inlet system. Monochromatic light with energy around the C 1s edge was generated by the TGM beamline at the Brazilian Synchrotron Facility. A Wiley-McLaren mass spectrometer was used to characterize and detect the ions formed by the camphor photoionization. The data analysis was supported by energy calculations.
Although the fragmentation patterns were basically the same at 270 eV and 330 eV, it was observed that above the C 1s edge the contribution to the spectrum from lower mass/charge fragment ions increased, pointing to a higher degree of dissociation of the molecule. Projections of the PEPIPICO spectra demonstrated the existence of unstable doubly charged species. The Gibbs free energy was calculated using the Møller-Plesset perturbation theory (MP2) for the neutral, singly and doubly excited camphor molecule.
Our PEPIPICO spectrum clearly demonstrated the formation of doubly ionic dissociative species. From a slope analysis, we propose a secondary decay after a deferred charge separation mechanism in which, after a few steps, the camphor dication dissociates into C2 H3 (+) and C3 H5 (+) . This is the main relaxation route observed at 270 eV and 330 eV. The large energy difference between the mono and the dication (of the order of 258.2 kcal/mol) may explain the experimentally observed absence of stable dications in the spectra, because their formation is disadvantaged energetically.
一类有趣的挥发性化合物——单萜类化合物存在于某些植物中，但其功能尚未完全明确。我们利用飞行时间质谱和符合技术研究了樟脑分子与单色高能光子（同步辐射）的相互作用。
将市售的S-樟脑样品未经纯化，通过进样系统引入真空腔室。巴西同步辐射装置的TGM光束线产生能量在C 1s边附近的单色光。使用威利-麦克拉伦质谱仪对樟脑光致电离形成的离子进行表征和检测。数据分析得到能量计算的支持。
尽管在270 eV和330 eV时的碎裂模式基本相同，但观察到在C 1s边以上，较低质荷比碎片离子对光谱的贡献增加，表明分子的解离程度更高。PEPIPICO光谱的投影显示存在不稳定的双电荷物种。使用莫勒-普列塞特微扰理论（MP2）计算了中性、单激发和双激发樟脑分子的吉布斯自由能。
我们的PEPIPICO光谱清楚地表明形成了双离子解离物种。通过斜率分析，我们提出了一种延迟电荷分离机制后的二次衰变机制，即经过几步后，樟脑二价阳离子解离为C2 H3(+)和C3 H5(+)。这是在270 eV和330 eV观察到的主要弛豫途径。单离子和二价阳离子之间的巨大能量差（约258.2 kcal/mol）可能解释了实验观察到的光谱中不存在稳定二价阳离子的现象，因为它们的形成在能量上是不利的。
