Chemical ionization in the atmosphere? A model study on negatively charged 鈥渆xotic鈥?ions generated from Titan's tholins by ultrahigh resolution MS and MS/MS

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• 作者：&Aacute ; rp&aacute ; d Somogyi^a ; ^{asomogyi@email.arizona.edu} ; Mark A. Smith^a ; Vé ; ronique Vuitton^b ; Roland Thissen^b ; Istv&aacute ; n Kom&aacute ; romi^c
• 关键词：Ultrahigh resolution MS ; MS/MS ; Titan tholins ; Negative ions ; Structural characterization
• 刊名：International Journal of Mass Spectrometry
• 出版年：2012
• 期刊代码：43_13873806
• 类别：ch
• 出版时间：15 April, 2012
• 卷：316-318
• 期：Complete
• 页码：157-163
• 文件大小：1152 K

摘要

Titan tholins generated by complex processes (including ion-molecule reactions) in a laboratory plasma were investigated by ultrahigh resolution MS and tandem MS/MS measurements. Titan has a special interest in astrobiology because 鈥渋n situ鈥?measurements by the Cassini-Huygens spacecraft indicate the presence of complex organic molecules of prebiotic interest. The present work focuses on negatively charged ions that have not been systematically studied by ultrahigh resolution MS and MS/MS. The negatively charged ions were generated from a tholin sample by both laser desorption ionization (LDI) and electrospray ionization (ESI). The chemical compositions determined for the negatively charged ions clearly indicate the presence of highly unsaturated (H/C < 1) species with high nitrogen content (presumably related to multiple cyano functionalities). This is characteristically different from the previously analyzed positively charged ions that are more saturated and contain amino and imino functionalities. Based on tandem MS/MS experiments and quantum chemical calculations we propose characteristic structural features for selected ions. They include open chain (C₆N₃^{鈭?/sup>) and aromatic ring structures (C₁₀N₅鈭?/sup>). The basic non-aromatic structural unit C₂N₃鈭?/sup> seems to play an important role and several structural 鈥渇amilies鈥?can be derived as HCN, HCCH and H₂ 鈥渁dducts鈥?of this ion.}