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Engineering

分子构象器和星团的空间分离

Published: January 09, 2014
doi:
10.3791/51137
, , , , , ,
1Center for Free-Electron Laser Science,CFEL, DESY, 2Department of Physics,University of Hamburg, 3The Hamburg Center for Ultrafast Imaging,University of Hamburg

Summary

我们提出了一种技术，允许分子束中存在的不同构象体或星团的空间分离。静电偏转器用于按质量与偶极时比将物种分开，从而产生单一构象器或聚类气相的气相合奏。

Abstract

气相分子物理和物理化学实验通常使用超音速膨胀通过脉冲阀门生产冷分子束。然而，这些光束通常包含多个构象和星团，即使在低旋转温度下也是如此。我们提出了一种实验方法，允许分子束膨胀的这些成分的空间分离。使用电动偏转器，光束按质量与偶极态的瞬时比分离，类似于弯管或电扇形质谱仪，根据质量与电荷比在空间上分散带电分子。这种偏转器利用了同质电场中的斯塔克效应，并允许分离单个物种的极性中性分子和星团。此外，它允许选择分子束中最冷的部分，因为低能旋转量子态通常经历最大的偏转。由于功能组的不同排列，物种的不同结构同构体（构造体）可以分离，从而导致不同的偶极时刻。这些被静电偏转器利用，用于从分子束中生成符合纯样品。同样，也可以选择特定的聚类测定，因为特定星团的质量和偶极时刻取决于母分子周围的沉降程度。这允许对特定的星团大小和结构进行实验，从而能够系统地研究中性分子的索尔夫。

Introduction

现代气相分子物理和物理化学实验通常使用目标分子的超音速膨胀在分子束内产生旋转冷分子样本。然而，即使在1K的低旋转温度下，大分子仍然可以在光束1内保持多个构象。同样，在光束源中产生分子簇不会导致单一物种，而是形成”聚类汤”，其中含有许多不同的聚类聚变，以及剩余的纯父分子。这使得对这些系统的研究变得困难，因为这些系统需要新的技术，如分子轨道2成像，分子帧光电子角分布3-5 或电子6-10 和X射线衍射11-13， 因为这些需要纯，一致，同质的样品在气体相。

虽然现在可用于在气相（如 离子移动漂移管14，15）中分离带电物种的不同构象体和带电聚类的带电聚类，但这些技术不适用于中性物种。我们最近证明，使用静电偏转装置16，17可以克服这些问题，从而能够分离分子构象器和星团，并产生旋转冷分子束。

静电偏转是一种经典的分子束技术，其起源可以追溯到18，19年。斯特恩于1926年20年提出了利用静电偏转分离量子态的第一个想法。虽然在高温下对小分子进行了早期实验，但我们证明了这项技术在16，21年低温下应用于大极分子和星团。

由于潜在能量的空间差异，极地分子在异质电场（E）内产生力。这种力 取决于分子的有效偶极极时刻，μ eff，可以评估为

(1)

由于不同的分子构象器通常具有不同的偶极态时刻和不同数量的溶剂分子在集群中导致不同的团团质量和偶极位，这些物种将经历不同的加速度在强大的同位素电场的存在。因此，来自同质电场的斯塔克效应力可用于构合体和量子态22的分离。这表示在图1中，显示计算的斯塔克曲线为J = 0，1，2旋转状态的cis和转符合 3 氟酚， 分别.这导致μ eff的巨大差异，如图1c和1d所示，因此两个符合者在异构电场中经历了不同的加速度。因此，静电偏转装置可用作质量与二极位的瞬间比（m/μ eff）分离器，与质谱仪类比，充当质量电荷比（m/z）滤波器23。

此外，这些技术允许旋转量子状态24，25的分离。由于地面旋转状态（ 图1a 和 1b中的蓝色曲线）显示最大的斯塔克移位，这些将偏转最多，可以在空间上从高 J 状态17的分子分离。因此，分子束中最冷的部分可以选择，显著有助于许多应用，如目标分子17、26-28的对齐和方向。

在这项贡献中，我们展示了静电偏转装置如何用于空间上分离不同种类的大型极地分子和星团。示例数据用于生成单个构象器的纯光束和定义明确的大小和比率的溶解剂集群。具体来说，我们提供3氟酚的数据，其中只含有转顺从器的纯光束，在鞋底水簇上，鞋底（H2O）1簇可以在空间上与水分离，鞋底，鞋底（H2O）2等。

Protocol

1. 实验设置的描述 气相分子束设置和偏转器的示意图显示在 图221中。它包括 含有分子样本的脉冲偶拉维阀29。 只要形成冷分子束（O（1 K），其他脉冲分子束阀就可以同样使用。以下参数是特定于使用偶拉维阀门的。在此处介绍的实验中，阀门以 20 Hz 重复率运行，背压高（氦在 50 酒吧），并扩展到真空室，疏散到< 10-6 mbar。 …

Representative Results

静电偏转技术已成功地应用于结构同构体16和中性星团21的分离，以及生产旋转量子态选定的分子样本31。我们用具有代表性的结果来证明这一点，即分离3氟酚的顺从和反式符合物，以及选定的尺寸（H2O）n集群。 3-氟酚符合者在分子束中与50根氦气的超音速膨胀分离。个别物种通过其独特的REMPI共振约272纳米32</s…

Discussion

在整个手稿中，假设熟悉超高真空组件、脉冲分子束阀门和激光源，并始终遵守相关的安全程序。在为偏转器处理高压电极时，需要特别小心。它们的表面需要抛光到高标准，并且必须绝对清洁，以避免在真空室内弧形。在首次使用之前，电极应在真空下调节。施加的电压缓慢增加，电流通过电极测量。电极不应绘制电流（最多按几个 nA 的顺序），与施加的电压无关。逐步增加应用电压的典型调理时间表如下：…

Disclosures

The authors have nothing to disclose.

Acknowledgements

这项工作得到了德国福雄斯格梅因沙夫特的卓越集群”汉堡超高速成像中心——原子尺度上的物质结构、动力学和控制”和赫尔姆霍尔茨虚拟研究所的”多维景观中的动态路径”的支持。

Materials

Vacuum system various, e.g. Pfeiffer Vacuum, Varian, Edwards, Leybold
Dye laser system various, e.g. Coherent, Spectra Physics, Syrah, LIOP-TEC, Radiant Dyes…
Pulsed valve Even-Lavie
High voltage power supply eg. FUG HCP 14-20000
Deflector Custom made
Time-of-flight spectrometer Jordan TOF C-677
TOF power supply Jordan TOF D-603
Focusing lens e.g. Thorlabs LA4745
Translation stage e.g. Vision Lasertechnik 8MT167-25
Digitizer e.g. Agilent Acquiris DC440
Digital delay generator e.g. Stanford Systems SRS DG645
Molecular beam skimmer Beam Dynamics Inc. http://www.beamdynamicsinc.com/
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Tags

Spatial SeparationMolecular ConformersMolecular ClustersSupersonic ExpansionsCold Molecular BeamsElectric DeflectorStark EffectMass-to-dipole Moment RatioConformational PurityCluster StoichiometrySolvationMolecular PhysicsPhysical Chemistry
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Horke, D., Trippel, S., Chang, Y., Stern, S., Mullins, T., Kierspel, T., Küpper, J. Spatial Separation of Molecular Conformers and Clusters. J. Vis. Exp. (83), e51137, doi:10.3791/51137 (2014).
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