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在大气压下对1,1 - 二氟乙烷(HFC - 152a)、1,1,1,2 - 四氟乙烷(HFC - 134a)和全氟正己烷(FC - 72)在空气等离子体中的正离子和负离子化学进行的大气压化学电离研究。

An atmospheric pressure chemical ionization study of the positive and negative ion chemistry of the hydrofluorocarbons 1,1-difluoroethane (HFC-152a) and 1,1,1,2-tetrafluoroethane (HFC-134a) and of perfluoro-n-hexane (FC-72) in air plasma at atmospheric pressure.

作者信息

Marotta Ester, Paradisi Cristina, Scorrano Gianfranco

机构信息

INTM del CNR-Sezione di Padova, Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padua, Italy.

出版信息

J Mass Spectrom. 2004 Jul;39(7):791-801. doi: 10.1002/jms.653.

Abstract

A report is given on the ionization/dissociation behavior of the title compounds within air plasmas produced by electrical corona discharges at atmospheric pressure: both positive and negative ions were investigated at different temperatures using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). CHF(2)CH(3) (HFC-152a) undergoes efficient ionic oxidation to C(2)H(5)O(+), in which the oxygen comes from water present in the plasma. In contrast, CF(3)CH(2)F (HFC-134a) does not produce any characteristic positive ion under APCI conditions, its presence within the plasma being revealed only as a neutral ligand in ion-molecule complexes with ions of the background (H(3)O(+) and NO(+)). Analogously, the perfluorocarbon FC-72 (n-C(6)F(14)) does not produce significant positive ions at 30 degrees C: at high temperature, however, it undergoes dissociative ionization to form many product ions including C(3)F(6)(+), C(2)F(4)(+), C(n)F(2n+1)(+) and a few families of oxygen containing cations (C(n)F(2n+1)OH(2)(+), C(n)F(2n)OH(+), C(n)F(2n-1)O(+), C(n)F(2n-1)O(2)H(2)(+), C(n)F(2n-2)O(2)H(+)) which are suggested to derive from C(n)F(2n+1)(+) in a cascade of steps initiated by condensation with water followed by steps of HF elimination and H(2)O addition. Negative ions formed from the fluoroethanes CHF(2)CH(3) and CF(3)CH(2)F (M) include complexes with ions of the background, O(2)(-)(M), O(3)(-)(M) and some higher complexes involving also water, and complexes of the fluoride ion, F(-)(H(2)O), F(-)(M) and higher complexes with both M and H(2)O also together. The interesting product O(2)(-)(HF) is also formed from 1,1-difluoroethane. In contrast to the HFCs, perfluoro-n-hexane gives stable molecular anions, M(-), which at low source temperature or in humidified air are also detected as hydrates, M(-)(H(2)O). In addition, in humidified air F(-)(H(2)O)(n) complexes are also formed. The reactions leading to all major positive and negative product ions are discussed also with reference to available thermochemical data and relevant literature reports. The effects on both positive and negative APCI spectra due to ion activation via increasing V(cone) are also reported and discussed: several interesting endothermic processes are observed under these conditions. The results provide important information on the role of ionic reactions in non-thermal plasma processes.

摘要

本文报道了在大气压下电晕放电产生的空气等离子体中标题化合物的电离/解离行为:使用大气压化学电离质谱(APCI-MS)在不同温度下对正离子和负离子进行了研究。CHF₂CH₃(HFC-152a)发生有效的离子氧化生成C₂H₅O⁺,其中的氧来自等离子体中的水。相比之下,CF₃CH₂F(HFC-134a)在APCI条件下不产生任何特征正离子,其在等离子体中的存在仅作为与背景离子(H₃O⁺和NO⁺)形成的离子-分子络合物中的中性配体被揭示。类似地,全氟碳化合物FC-72(n-C₆F₁₄)在30℃时不产生显著的正离子:然而,在高温下,它发生解离电离形成许多产物离子,包括C₃F₆⁺、C₂F₄⁺、CₙF₂ₙ₊₁⁺以及一些含氧化阳离子家族(CₙF₂ₙ₊₁OH₂⁺、CₙF₂ₙOH⁺、CₙF₂ₙ₋₁O⁺、CₙF₂ₙ₋₁O₂H₂⁺、CₙF₂ₙ₋₂O₂H⁺),这些离子被认为是由CₙF₂ₙ₊₁⁺通过与水缩合引发的一系列步骤,随后是HF消除和H₂O添加步骤形成的。由氟乙烷CHF₂CH₃和CF₃CH₂F(M)形成的负离子包括与背景离子的络合物O₂⁻(M)、O₃⁻(M)以及一些还涉及水的更高阶络合物,还有氟离子的络合物F⁻(H₂O)、F⁻(M)以及同时与M和H₂O形成的更高阶络合物。有趣的产物O₂⁻(HF)也由1,1 - 二氟乙烷形成。与氢氟碳化合物不同,全氟正己烷产生稳定的分子阴离子M⁻,在低源温度或潮湿空气中也被检测为水合物M⁻(H₂O)。此外,在潮湿空气中还形成了F⁻(H₂O)ₙ络合物。还参考现有的热化学数据和相关文献报道讨论了导致所有主要正、负产物离子的反应。还报道并讨论了通过增加V(cone)进行离子活化对正、负APCI光谱的影响:在这些条件下观察到了几个有趣的吸热过程。这些结果为离子反应在非热等离子体过程中的作用提供了重要信息。

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