Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

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• 作者：Christine J. Koh ; Chen-Lin Liu ; Christopher W. Harmon ; Daniel Strasser ; Amir Golan ; Oleg Kostko ; Steven D. Chambreau ; Ghanshyam L. Vaghjiani ; Stephen R. Leone
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：May 12, 2011
• 年：2011
• 卷：115
• 期：18
• 页码：4630-4635
• 全文大小：847K
• 年卷期：v.115,no.18(May 12, 2011)
• ISSN：1520-5215

文摘

Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim⁺][Tf₂N^{鈥?/sup>]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim+][Dca鈥?/sup>]), are generated by vaporizing ionic liquid submicrometer aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim+ and Bmim+, presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Photoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim+][Tf₂N鈥?/sup>] ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (0.3 eV), attributed to reduced internal energy of the isolated ion pairs. The method of ionic liquid submicrometer aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally 鈥渃ooler鈥?source of isolated intact ion pairs in the gas phase compared to effusive sources.}