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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Inverse heavy-atom kinetic isotope effects in chloroalkanes
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Inverse heavy-atom kinetic isotope effects in chloroalkanes

机译：氯代烷烃中重原子动力学同位素的反作用

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Intramolecular heavy-atom kinetic isotope effects (KIEs) are reported for reactions of some gas-phase ions relevant to atmospheric chemistry. The anionic complexes carbon tetrachloride/Cl-, chloroform/Cl-, and methylene chloride/Cl- (CHnCl5-n-; n = 0-2) were generated by various ionization methods and subjected to single-stage and tandem mass spectrometric analysis in a variety of instruments. Strongly pressure dependent, anomalous chloride abundances were observed in single-stage mass spectra under self-chemical ionization conditions for CHCl4- and CCl5- in a triple quadrupole and for CHCl4- in a quadrupole ion trap. Further examination of these complexes in triple quadrupole MS/MS experiments confirmed the presence of an unusually large inverse kinetic isotope effect. We suggest that the selective loss of Cl-37(-) is simply due to the difference in centrifugal barriers associated with the competitive reaction channels leading to the two chloride isotopes. This effect is greatly magnified near the threshold for dissociation, and an extreme value of an inverse kinetic isotope effect (0.026 +/- 0.01) is displayed by the isotopomeric chloride adduct of chloroform, (CHCl3Cl-)-Cl-35-Cl-37, under single-collision conditions with xenon at 27 eV lab collision energy. The methylene chloride adduct, (CH2Cl2Cl-)-Cl-35-Cl-37, had a KIE close to unity (0.90 +/- 0.05), and the carbon tetrachloride adduct displayed no apparent KIE, under these same conditions. Remarkably, in addition to the heavy-atom KIEs for chlorinated chloroform, (i) substantial HID isotope effects are associated with chloride loss, (ii) the chlorine KIE values are strongly dependent on the particular isotopomer selected for examination, and (iii) the chlorine KIE for CHCl4- is not monotonic with collision energy. In sum, the results are indicative of a complex potential energy surface and of a mixture of dissociating structures or independent dissociation channels of the precursor.
机译：据报道，与大气化学有关的某些气相离子的反应具有分子内重原子动力学同位素效应（KIE）。通过各种电离方法生成四氯化碳/ Cl-，氯仿/ Cl-和二氯甲烷/ Cl-（CHnCl5-n-; n = 0-2）的阴离子络合物，并进行单级串联质谱分析。各种乐器。在自化学电离条件下，在三级四极杆中的CHCl4-和CCl5-和在四极杆离子阱中的CHCl4-，在自化学电离条件下的单级质谱图中观察到了强烈的压力依赖性氯化物反常丰度。在三重四极杆MS / MS实验中进一步检查了这些配合物，证实了存在异常大的逆动力学同位素效应。我们建议，Cl-37（-）的选择性损失仅是由于与导致两个氯同位素的竞争性反应通道相关的离心屏障的差异所致。在离解阈值附近，该效应被大大放大，并且氯仿的（CHCl3Cl-）-Cl-35-Cl-37的异聚氯化物加合物显示出逆动力学同位素效应的极值（0.026 +/- 0.01）。在单次碰撞条件下，氙气在27 eV的实验室碰撞能量下发生。在这些相同条件下，二氯甲烷加合物（CH2Cl2Cl-）-Cl-35-Cl-37的KIE接近于统一（0.90 +/- 0.05），四氯化碳加合物没有表现出明显的KIE。值得注意的是，除了氯化氯仿的重原子KIE之外，（i）大量的HID同位素效应还与氯化物的损失有关;（ii）氯的KIE值强烈依赖于所选择的特定同位素，并且（iii） CHCl4-的氯KIE与碰撞能量不是单调的。总而言之，该结果指示了复杂的势能表面以及前体的解离结构或独立的解离通道的混合物。

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