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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Fragmentation of Allylmethylsulfide by chemical ionization: Dependence on humidity and inhibiting role of water
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Fragmentation of Allylmethylsulfide by chemical ionization: Dependence on humidity and inhibiting role of water

机译：化学电离作用分解烯丙基甲基硫：取决于湿度和水的抑制作用

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摘要

We report on a previously unknown reaction mechanism involving water in the fragmentation reaction following chemical ionization. This result stems from a study presented here on the humidity-dependent and energy-dependent endoergic fragmentation of allyl methyl sulfide (AMS) upon protonation in a proton transfer reaction-mass spectrometer (PTR-MS). The fragmentation pathways were studied with experimental (PTR-MS) and quantum chemical methods (polarizable continuum model (PCM), microhydration, studied at the MP2/6-311+G(3df,2p)//MP2/ 6-31G(d,p) level of theory). We report in detail on the energy profiles, reaction mechanisms, and proton affinities (G4MP2 calculations). In the discovered reaction mechanism, water reduces the fragmentation of protonated species in chemical ionization. It does so by direct interaction with the protonated species via covalent binding (C_3H_5~+) or via association (AMS·H~+). This stabilizes intermediate complexes and thus overall increases the activation energy for fragmentation. Water thereby acts as a reusable inhibitor (anticatalyst) in chemical ionization. Moreover, according to the quantum chemical (QC) results, when water is present in abundance it has the opposite effect and enhances fragmentation. The underlying reason is a concentration-dependent change in the reaction principle from active inhibition of fragmentation to solvation, which then enhances fragmentation. This amphoteric behavior of water is found for the fragmentation of C_3H_5 + to C_3H _3~+, and similarly for the fragmentation of AMS·H~+ to C_3H_5 ~+. The results support humidity-dependent quantification efforts for PTR-MS and chemical ionization mass spectrometry (CIMS). Moreover, the results should allow for a better understanding of ion-chemistry in the presence of water.
机译：我们报告了以前未知的反应机理，其中涉及水在化学电离后的裂解反应中。该结果源自此处提出的一项研究，该研究涉及质子转移反应质谱仪（PTR-MS）中质子化后烯丙基甲基硫醚（AMS）的湿度依赖性和能量依赖性内能碎裂。使用实验（PTR-MS）和量子化学方法（极化连续谱模型（PCM），微水化，在MP2 / 6-311 + G（3df，2p）// MP2 / 6-31G（d ，p）理论水平）。我们详细报告了能量分布，反应机理和质子亲和力（G4MP2计算）。在已发现的反应机理中，水减少了化学电离过程中质子化物质的破碎。它是通过共价结合（C_3H_5〜+）或通过缔合（AMS·H〜+）与质子化物种直接相互作用来实现的。这使中间体复合物稳定，因此总体上增加了断裂的活化能。水因此在化学电离中充当可重复使用的抑制剂（抗催化剂）。此外，根据量子化学（QC）结果，当水大量存在时，它具有相反的作用并增强碎裂。根本原因是反应原理中浓度依赖性的变化，从主动抑制断裂到溶剂化，然后增强了断裂。发现水的这种两性行为是C_3H_5 +碎裂为C_3H _3〜+，类似地是AMS·H〜+碎裂为C_3H_5〜+。结果支持PTR-MS和化学电离质谱（CIMS）依赖于湿度的定量工作。此外，结果应有助于更好地理解在水存在下的离子化学。

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