强场绝热电离多原子自由基阳离子超快振动相干的测量
Summary
我们提出了一个方法来探测超快振动相干的原子基阳离子, 导致分子离解。
Abstract
提出了一种在多原子自由基阳离子中制备振动相干的泵探针法, 并对其超快动力学进行了探讨。通过将强场电离泵脉冲的波长从常用的 800 nm 转换为近红外 (1200-1600 nm), 绝热电子隧穿对电离过程的贡献相对于多光子吸收增加。绝热电离结果在电子去除时, 离子的地面电子状态的主要人口, 有效地准备一个连贯的振动状态 (“波浪分组”) 服从随后励磁。在实验中, 用弱场 800 nm 脉冲和在飞行时间质谱仪中测量的离解产物的时间依赖率来探测相干振动动力学。我们提出了分子二甲基磷酸 (DMMP) 的测量, 以说明如何使用 1500 nm 脉冲来提高离子产生相干振荡的振幅, 其系数为 10, 与 800 nm 脉冲相比。本协议可在现有的水泵探头设置中实现, 方法是将光学参量放大器 (.) 引入波长转换。
Introduction
自1960年激光发明以来, 有选择地打破分子中化学键的目标一直是化学家和物理学家的长期梦想。据信, 调整激光频率和强度的能力, 使目标键通过选择性能吸收在相关的振动频率1,2,3,4 的直接劈裂..然而, 早期的实验发现, 分子内的吸收能量的分子内振动再分配往往导致最弱键4,5的非选择性解切。直到飞秒脉冲激光器的发展和泵探针技术6在1980后期, 直接操纵相干振动状态, 或 “波包”, 成功地控制了键分裂和其他目标6、7、8。泵探头测量, 其中 “泵” 脉冲准备一个兴奋的状态或离子, 随后被延迟的 “探针” 脉冲激发, 仍然是最广泛使用的技术研究分子9的超快过程, 10,11,12,13,14,15,16,17,18, 19,20。
用泵-探针激发耦合质谱检测法研究多原子自由基阳离子超快离解动力学的一个重要局限性是由电离泵非选择性靶分子的碎片化产生的。脉冲在 Ti: 蓝宝石波长800毫微米21,22,23。这种过剩的碎片起因于非绝热多光子电离, 可以通过将激发波长转换为近红外线 (e., 1200-1500 nm)22,23,24, 来减轻 25。在这些较长的波长, 绝热电子隧穿的贡献相对于多光子激发在电离过程22,23。绝热隧道给分子和形成主要地 “冷的地面状态分子离子19,22,23给少量多余的能量。我们以前的研究表明, 近红外激发的使用大大改善了相干振动激发的制备, 或 “波包”, 在多原子自由基阳离子中, 与 800 nm 激发19相比, 20。这项工作将说明用 1500 nm 和 800 nm 在化学战剂模拟二甲磷酸 (DMMP) 上进行的泵探针测量, 以多光子为主的强场电离与隧道贡献的区别。泵波长。
在我们的泵探针实验中, 一对超短激光脉冲是时间延迟, 重组, 并聚焦到飞行时间的质谱仪, 如图 1中的设置所示。这些实验需要钛: 蓝宝石再生放大器生产 > 2 兆焦耳, 800 毫微米, 30 fs 脉冲。放大器输出在 90:10 (%R:%T) 光束分配器上拆分, 其中大部分能量用于为 1200年-1600 nm、100-300 µJ、20-30 fs 脉冲的生成提供一个光学参量放大器。红外泵束的直径扩展到22毫米, 800 nm 探针光束的直径向下-准直至5.5 毫米, 并使用虹膜进行芯核。这些 collimations 导致泵束聚焦于明显较小的束腰 (9 µm) 比探头束 (30 µm), 从而确保在电离泵脉冲形成的所有离子被延时探针脉冲激发。使用这种配置是因为我们的实验目的是探索母体分子离子的动力学, 即使是在聚焦光束边缘附近的较低强度下也可以形成。我们注意到, 如果更多的高激发离子物种的动力学是感兴趣的, 那么探头的光束直径应该比泵更小。
泵和探针脉冲传播 collinearly, 并集中在提取区域的威利-迈凯轮飞行时间质谱仪 (26 ) (图 2)。分子样品放置在一个小瓶连接到入口, 并打开到真空。此设置要求正在调查的分子具有非零的蒸气压;对于低蒸气压的分子, 瓶子可能会加热。气体样品流入燃烧室的流量由两个可变泄漏阀控制。样品进入房间通过一个 1/16 “不锈钢管大约 1 cm 离激光焦点 (图 2) 为了交付一个地方高集中目标分子在提取区域27。该萃取板有一个0.5 毫米狭缝定向正交到激光传播和离子路径。由于泵浦光束的瑞利范围约为2毫米, 这一狭缝用作过滤器, 只允许从中心焦量产生的离子, 在强度最高的情况下通过萃取板28。离子进入1米无场漂移管, 以达到 Z 隙微通道板 (MCP) 探测器29, 在那里他们被发现, 并记录与 1 GHz 数字示波器在1赫重复率的典型商业 Ti: 蓝宝石激光器。
Protocol
注: 所有商业获得的仪器和零件, 如激光, 真空泵, 室, 飞行时间管和微通道板检测器是根据制造商的说明或用户手册安装和操作。激光安全护目镜设计的操作激光强度和波长应佩戴。 1. 施工26毫秒 设计和建造一个超高真空 (特高压) 室, 有足够的空间容纳标准的离子光学26和规定安装在2¾ “法兰上的光学窗口的任何一侧的离子光学 (<stron…
Representative Results
给出了21分子 DMMP 的结果。图 3显示了在零时间延迟时以 1500 nm 泵的峰值强度和 800 nm 探针脉冲分别为 8 x 1013和 8 x 1012 W 厘米-2的 DMMP 质谱。为参考, 还显示了仅用泵浦脉冲的质量谱。光谱是平均1万激光射击 (总承购时间十二年代)。当泵与探头梁之间的空间重叠优化 (绿色光谱) 时, 标记为 * 的离子信号的增加?…
Discussion
该协议使我们能够通过选择性地在基态电子态中制备离子来解决原子基阳离子中的超快振动动力学问题。当标准强场电离过程使用800毫微米能准备振动相干在地线电子状态根本阳离子第一列 diatomics10,11,12,13并且 CO214,15, 多原子离子中多个离子激发态?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作得到了美国陆军研究办公室的支持, 通过合同 W911NF-18-1-0051。
Materials
| Mass spectrometer components | |||
| TOF lens stack and flight tube assembly | Jordan TOF Products, Inc. | C-677 | |
| 18 mm Z-gap detector assembly | Jordan TOF Products, Inc. | C-701Z | |
| TOF high voltage power supply | Jordan TOF Products, Inc. | D-603 | |
| Vacuum system components | |||
| Rotary vane backing pump | Edwards Vacuum LLC | RV12 | |
| Turbomolecular pumps (2) | Edwards Vacuum LLC | EXT255H | |
| Turbomolecular pump controllers (2) | Edwards Vacuum LLC | EXC300 | |
| Pressure gauge | Edwards Vacuum LLC | AIGX-S-DN40CF | |
| Chiller for water cooling | Neslab | CFT-25 | |
| Femtosecond laser system | |||
| Ti:Sapphire regenerative amplifier | Coherent, Inc. | Astrella | oscillator and amplifier in a single integrated system |
| Optical Parametric Amplifer (OPA) | Light Conversion | TOPAS Prime | |
| Motion control | |||
| Motorized linear translation stage 1" travel | Thorlabs | Z825B | |
| controller for linear translation stage | Thorlabs | KDC 101 | |
| USB controller hub and power supply | Thorlabs | KCH 601 | |
| Manual linear translation stage 1" travel | Thorlabs | PT1 | |
| Detectors | |||
| Pyroelectric laser energy meter | Coherent, Inc. | 1168337 | |
| Thermal laser power meter | Coherent, Inc. | 5356E16R | |
| Si-biased detector 200-1100 nm | Thorlabs | DET10A | |
| Compact USB CMOS Camera | Thorlabs | DCC1545M | |
| USB spectrometer | Ocean Optics | HR4000 | |
| 1 GHz digital oscilloscope | LeCroy | WaveRunner 610Zi | |
| Optics | |||
| Type 1 BBO crystal | Crylight Photonics | BBO007 | aperture and thickness may be customized |
| Achromatic half wave plate, 1100-2000 nm | Thorlabs | AHWP05M-1600 | |
| Wollaston prism polarizer | Thorlabs | WPM10 | |
| Hollow retro-reflector | PLX, Inc. | OW-20-1C | |
| Variable neutral density filter | Thorlabs | NDC-100C-2 | |
| Longpass dichroic mirror 2" diameter | Thorlabs | DMLP950L | |
| Software | |||
| Digital Camera image software | Thorlabs | ThorCam | |
| Instrument communication interface | National Instruments | NI-MAX | |
| Graphical development environment for measurement programs | National Instruments | LabVIEW | |
| Data processing software | Mathworks | MATLAB |
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Cite This Article
Ampadu Boateng, D., Tibbetts, K. M. Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization. J. Vis. Exp. (138), e58263, doi:10.3791/58263 (2018).