Probing the structure of CH5+ ions and deuterated variants via collisions.
Probing the structure of CH5+ ions and deuterated variants via collisions.
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通过碰撞探测 CH5 离子和氘代变体的结构。
DOI：
10.1039/b419328h
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
D. Gerlich
中科院分区：
文献类型：
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作者：
D. Gerlich
许多最近的计算提供了一个相当详细的图片质子化的甲烷，CHS+，真的可能看起来像在非常低的温度;然而，还没有任何实验，提供信息的相关性的结构，这种fluxional离子与状态之间的过渡引起的光子或碰撞。光谱学和质谱学的各种努力为这个难题做出了重要的贡献，但没有真实的最终结论，例如，C-H伸缩振动区域的红外光谱几年来一直在等待分配。这篇文章回顾并讨论了各种详细的碰撞实验的潜力和局限性，以了解更多关于质子化甲烷和氘代变体，无论是通过创建，修改或破坏CH 5+。有一个实验似乎表明，从CD 4+到CH 4的氘转移可以产生稳定的同位素异构体，具有化学上可区分的氢原子，CH 3-HD+。使用复杂的离子束技术测量的详细积分和微分截面揭示了有趣的动力学;但不幸的是，CH 5+的形成肯定比简单的质子转移到稳定的异构体更加复杂。在CH 4+与CH 4或CD 4的碰撞中，存在显著的混乱，并且需要使用差分散射选择来获得仅通过特定机制产生的离子。已经有几个低温离子阱研究导致CH 5+，例如，简单地通过CH 3+与H2的辐射缔合或通过CH 4（+）+ H2碰撞中的氢提取。在低温碰撞中使用氘化变体进行了非常有趣的和在某些情况下不可预见的观察。一般的结论是，H-D交换不仅受零点能量差异的影响，而且对称性选择规则可以显着限制置乱。例如，核自旋守恒可以允许通过辐射缔合用局部邻位氢旋转体合成特定的CD 3 H2+离子。冷捕获的CH 5+离子已探测与HD碰撞。尽管捕获技术的灵敏度很高，但完全没有观察到H-D交换，而一些同位素当量的CH 7+通过辐射缔合生长。最后，我们最近的活动简要地提到，探测冷离子通过碰撞慢H或D原子。本调查以结论和展望结束。可以肯定的是，所有传统的碰撞探测方法都无法提供不同的CH 5+异构体的证据。然而，如果光谱学，低温碰撞动力学，多电极陷阱和超声或溢出束以适当的方式相结合，可以成功地探测在低温下的未扰动冷离子的单态。
Numerous recent calculations have provided a rather detailed picture how the protonated methane, CHS+, really may look like at very low temperatures; however, there is not yet any experiment, providing information on the correlation of a structure of this fluxional ion with a state to state transition induced by a photon or a collision. Various efforts in spectroscopy and mass spectrometry have contributed important pieces to the puzzle but there are no real final conclusions, e.g. infrared spectra in the region of the C-H stretching vibration are waiting for assignment since several years. This contribution reviews and discusses the potential and the limitations of a variety of detailed collision experiments for learning more about protonated methane and deuterated variants, either via creation, modification or destruction of CH5+. There has been a controversial discussion about an experiment which seemed to indicate that deuteron transfer from CD4+ to CH4 can create stable isotopomers with chemically distinguishable hydrogen atoms, CH3-HD+. Detailed integral and differential cross sections measured with sophisticated ion beam techniques revealed interesting dynamics; but, unfortunately, CH5+ formation is certainly more complicated than just a simple proton transfer into a stable isomer. In collisions of CH4+ with CH4 or CD4, there is significant scrambling and one would need to use differential scattering selection for getting ions produced exclusively via a specific mechanism. There have been several low temperature ion trap studies leading to CH5+, e.g., simply via radiative association of CH3+ with H2 or via hydrogen abstraction in CH4(+) + H2 collisions. Very interesting and in some cases unforeseen observations have been made by using deuterated variants in low temperature collisions. A general conclusion is that H-D exchange is not only influenced by the differences in zero point energies but that symmetry selection rules can significantly restrict the scrambling. For example, conservation of nuclear spin may allow one to synthesize specific CD3H2+ ions with a local ortho hydrogen rotator via radiative association. Cold trapped CH5+ ions have been probed by collisions with HD. Despite the high sensitivity of the trapping technique, no H-D exchange could be observed at all while a few isotopic equivalents of CH7+ grow via radiative association. Finally, our most recent activities are briefly mentioned, probing cold CHR+ ions via collisions with slow H or D atoms. This survey ends with a conclusion and an outlook. It is very sure that all traditional methods of collisional probing are unable to provide evidence for different CH5+ isomers. If, however, spectroscopy, low temperature collision dynamics, multi-electrode traps and supersonic or effusive beams are combined in a suitable way, one may succeed in probing single states of unperturbed cold ions at low temperatures.