NH4+ Association and Proton Transfer Reactions With a Series of Organic Molecules
NH4+ Association and Proton Transfer Reactions With a Series of Organic Molecules
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DOI：
10.3389/fchem.2019.00191
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发表时间：
2019-04-03
影响因子：
5.5
通讯作者：
Hansel, Armin
中科院分区：
文献类型：
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作者：
Canaval, Eva;Hyttinen, Noora;Hansel, Armin
在这项研究中，我们用选择性试剂电离飞行时间质谱仪(SRI-TOF-MS)研究了NH(4)(+)与一系列分析物(A)：丙酮(C3H6O)、甲基乙烯基酮(C4H6O)、甲乙酮(C4H8O)和八种单萜异构体(C10H16)的反应。我们研究了碰撞能分别为55 meV和80 meV的离子-分子反应。酮具有比NH3低得多的质子亲和力，在55 meV时仅产生可检测数量的团簇离子NH4+(A)。在80 meV时，没有检测到团簇离子，这意味着这些加合物是由强烈依赖温度的缔合反应形成的。大多数单萜的团簇离子的键能和质子亲和能都是未知的，都是通过高水平的量子化学计算得到的。计算揭示了单萜的质子亲和力，其范围从略小到实质上高于NH3的质子亲和力。质子亲和力和团簇键能允许将单萜作为解离反应NH(4)(+)A->；AH(+)+NH3的焓的函数进行分组。我们发现这一热可以用来预测NH4+(A)团簇离子的产额。本研究解释了涉及NH4+离子化学的产物离子的形成。这对于利用NH4+和NH4+(H2O)作为试剂离子的化学电离质谱仪(CIMS)实时定量检测大气中重要的有机化合物具有重要意义。
In this study, we present reactions of NH(4)(+ )with a series of analytes (A): acetone (C3H6O), methyl vinyl ketone (C4H6O), methyl ethyl ketone (C4H8O), and eight monoterpene isomers (C10H16) using a Selective Reagent Ionization Time-of-Flight Mass Spectrometer (SRI-ToF-MS). We studied the ion-molecule reactions at collision energies of 55 and 80 meV. The ketones, having a substantially lower proton affinity than NH3, produce only cluster ions NH4+(A) in detectable amounts at 55 meV. At 80 meV, no cluster ions were detected meaning that these adductions are formed by strongly temperature dependent association reactions. Bond energies of cluster ions and proton affinities for most monoterpenes are not known and were estimated by high level quantum chemical calculations. The calculations reveal monoterpene proton affinities, which range from slightly smaller to substantially higher than the proton affinity of NH3. Proton affinities and cluster bond energies allow to group the monoterpenes as a function of the enthalpy for the dissociation reaction NH(4)(+)A -> AH(+) + NH3. We find that this enthalpy can be used to predict the NH4+(A) cluster ion yield. The present study explains product ion formation involving NH4+ ion chemistry. This is of importance for chemical ionization mass spectrometry (CIMS) utilizing NH4+ as well as NH4+(H2O) as reagent ions to quantitatively detect atmospherically important organic compounds in real-time.