Department of Chemistry, University of California, Berkeley, California 94720, United States.
J Phys Chem A. 2011 May 12;115(18):4630-5. doi: 10.1021/jp200633b. Epub 2011 Apr 20.
Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim(+)][Tf(2)N(-)]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim(+)][Dca(-)]), 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(+)][Tf(2)N(-)] 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 "cooler" source of isolated intact ion pairs in the gas phase compared to effusive sources.
首次通过蒸发离子液体亚微米气溶胶颗粒来生成常规离子液体 1-乙基-3-甲基咪唑双（三氟甲烷磺酰基）亚胺 ([Emim(+)][Tf(2)N(-)]) 和反应性富燃离子液体 1-丁基-3-甲基咪唑二氰胺 ([Bmim(+)][Dca(-)]) 的孤立离子对；通过可调谐真空紫外 (VUV) 光的离解电离来研究蒸发物种，显示出清晰完整的阳离子 Emim(+) 和 Bmim(+)，可能源自完整的离子对。富燃离子液体扩散源的离子对蒸气的质谱显示由于源自源的分子的内部能量而发生大量的反应性分解。比较气溶胶源和扩散源的 [Emim(+)][Tf(2)N(-)] 离子液体蒸气中孤立离子对的近阈电离区光电离效率曲线，由于离子对中的内部能量的变化而导致出现能的变化。气溶胶源的阈值能量（约 0.3 eV）发生偏移，这归因于孤立离子对中的内部能量降低。与扩散源相比，对于反应性离子液体（如富燃物质），离子液体亚微米气溶胶颗粒蒸发的方法是一种方便、热“冷却”的气相中完整孤立离子对的源。
