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。

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
<ol><li>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 (图 1)。</li>
	<li>将1米飞行管上安装的离子光学束连接到燃烧室。 注意: 为了节省光学表上的空间, 垂直安装离子光学和飞行管是最容易的。</li>
	<li>将1/16 不锈钢管插入萃取器和驱板之间的腔内, 将管子从腔体中取出, 并将其连接至¼ "不锈钢管27。将一个或多个可变泄漏阀附加到¼ "不锈钢管" 中。 注: 可将含有分子样品或气罐的玻璃管附着在取样入口的导管上。</li>
	<li>将18毫米微通道板栈安装在 Z 堆栈配置29上, 在飞行管的末端。</li>
	<li>将两个光学窗口 (1 毫米厚度, 50 毫米直径, 熔融二氧化硅) 安装在2¾ "法兰上的房间。 注: 激光束通过这两个窗口通过驱和萃取板之间的空间传播。</li>
	<li>通过电流贯穿件可和 BNC 电缆将离子光学和探测器连接到高压电源。</li>
	<li>将一涡轮分子泵连接到离子光学附近的腔室, 再将第二泵安装到探测器附近的飞行管末端 (图 1)。将两个泵连接到适当的后备泵。 注意: 当将涡轮分子泵连接到垂直安装的飞行管的末端时, 注意确保系统不会由于泵的重量而倾斜到一侧。通过将真空室连接到光学表, 可以减轻此问题。</li>
	<li>打开水泵, 等待24小时。室内压力应低于 10-8乇, 无样品。如果压力高, 检查泄漏和拧紧螺母或烘烤室, 直到达到预期的压力。</li>
</ol>2. 光学泵和探头路径的构建
注:图 1给出了泵和探头光学路径的示意图。
<ol><li>提供飞秒激光脉冲 注: 飞秒激光脉冲 (800 nm) 是由商业 Ti: 蓝宝石再生放大器源操作, 根据制造商的手册。<ol>
<li>打开激光, 等待约30分钟, 使其稳定。</li>
		<li>位置 90:10 (%R:%T) 光束分配器后, 激光输出产生两个副本, 这将用于构造泵和探头光束线。检查两个副本的激光功率, 以确保足够的电源交付。</li>
		<li>将反射光束定向到光参量放大器中, 并利用本手册中的程序对输出功率进行优化。</li>
	</ol>
</li>
	<li>泵浦光路的制备<ol>
<li>设置可选的软件以选择所需的波长。</li>
		<li>通过λ/2 波板 (WP) 和偏光片 (P) 直接将输出光束从通过。</li>
		<li>阻挡 p 偏振光束, 并将 s-偏振光束定向到凹 (f =-10 厘米) 和凸 (f = 50 厘米) 镜面, 以5的系数扩大其直径。</li>
		<li>将展开的光束定向到分色镜 (DC)。</li>
	</ol>
</li>
	<li>探针光路的制备<ol>
<li>将通过90:10 光束拆分器的光束定向到凸镜 (f = 20 厘米) 和凹镜 (f =-10 厘米), 以减小其直径 (以2为因子)。</li>
		<li>将向下准直光束定向到安装在机动线性延迟阶段的空心复古反射器。在复古反射镜前调整两个平面镜的安装旋钮, 以确保当舞台沿其完整的行程移动时, 后反光反射器的光束位置不会发生变化。 注意: 这可以确保泵探头的空间重叠将保持在整个扫描范围内。</li>
		<li>在延迟阶段后插入可调谐中性密度 (ND) 滤波器, 以减弱探头脉冲的功率, 在 ND 滤波器后插入虹膜以调整光束直径, 并将光束定向到分色镜 (DC)。</li>
	</ol>
</li>
	<li>泵和探头脉冲持续时间的测量 注: 泵和探头脉冲的持续时间用内置的第二谐波产生-频率分辨光门 (SHG) 设置来测量。关于 SHG 青蛙的设置, 测量过程和数据检索算法的构造的细节在别处被描述30,31,32。在我们的实验中, 输出的脉冲持续时间通常是大约 20 fs 和 800 nm 脉冲约 30 fs19,20,27。然而, OPAs 可以引入高阶脉冲畸变, 因此, 可能需要实现脉冲压缩, 例如, 啁啾镜像10,11,12,13或声光调制器16。<ol>
<li>堵塞泵或探头梁。把剩下的光束直接放到青蛙里, 用平镜放置在混合了泵和探针脉冲的分色镜之后。</li>
		<li>确保两束在β钡硼酸盐 (BBO) 晶体中的青蛙重叠。调整光束对准和延迟阶段, 直到第三束在两个原梁之间可见。</li>
		<li>用虹膜和f = 10 cm 透镜, 隔绝并且聚焦光束入连接到光谱仪和计算机的光纤装载。</li>
		<li>采集青蛙扫描, 用相应的软件和检索算法检索脉冲形状。</li>
		<li>重复步骤 2.4. 1-2. 4.3 为另一束。取下镜子, 把光束引向青蛙。</li>
	</ol>
</li>
	<li>泵与探头梁的粗空间重叠 注: 如果泵和探头光束可见, 则可以跳过步骤2.5.1。<ol>
<li>在分色后插入15毫米直径的 BBO 晶体, 双光束的波长加倍, 从而使它们可见。 注: 这是最容易使用的一个 1200-1300 nm 的激光测量波长, 使一个橙色 600-650 nm 光束, 很容易区分从蓝色 400 nm 探针光束。注意确保泵束最密集的区域通过晶体的中心。晶体的角度应该优化, 使橙色和蓝色的脉冲很容易看到, 虽然这个角度可能不对应的最大强度的给定颜色。</li>
		<li>调整泵和探头光束对齐, 使用前镜安装在分色, 使光束传播 collinearly 通过飞行-MS 室和从另一侧。 注: 探头光束直径较小, 应集中在泵梁的中间。</li>
	</ol>
</li>
	<li>泵与探头梁的粗糙时间重叠 注: 此处描述的方法仅限于示波器分辨率, 只能在延迟阶段的几毫米行程内确定零延迟位置。<ol>
<li>在泵和探头横梁的路径中, 将一个快速光电二极管探测器放在窗口入口前几厘米处。将探测器电缆连接到数字示波器, 并独立定位泵和探头脉冲的信号。</li>
		<li>调整机动延迟阶段在探头线上的位置, 这样在示波器中的泵和探头信号会被世俗地重叠。如果一个信号一直在前面 (后面) 的另一个在示波器, 移动装载持有机动延迟阶段, 以缩短或延长路径长度根据需要。</li>
		<li>卸下光电二极管探测器。</li>
	</ol>
</li>
</ol>3. 初步测量
注: 我们实验中的所有数据都是使用商用仪表控制软件 (材料表) 内部编写的代码获取的。所有仪器驱动软件都是从各自的制造商那里获得的。
<ol><li>泵浦脉冲绝对峰值强度的标定28<ol>
<li>阻挡探头光束, 在入口窗前直接插入f = 20 厘米透镜安装在一个手动的线性平移阶段。</li>
		<li>调整波形板 (WP) 旋转角度 (图 1), 以最大限度地提高泵浦光束在镜头前的功率。</li>
		<li>将一罐氙气气体连接到飞行通道-MS 室入口, 并调整泄漏阀控制气体流向燃烧室, 使压力表读数介于 5-10 x 10-8乇之间。在调整采样压力时, 要确保时间-MS 电源电压熄灭, 以避免由于压力峰值引起的 MCP 探测器损坏。</li>
		<li>将 MCP 探测器和激光信号延迟发生器的输出电缆连接到数字示波器。设置示波器触发激光信号。</li>
		<li>打开 "MS" 电源, 检查电压。v1、v2、v3和 v4 (图 2) 的电压的典型值分别为 +4,190 v、+3,910 v、0 v 和-3,000 v。</li>
		<li>在示波器中直接或通过连接到示波器的计算机检查氙+ (和较高电荷状态) 的离子信号。</li>
		<li>调整手持透镜的手动平移阶段的位置, 使总离子信号最大化。这一步确保泵束聚焦与图 2所示的0.5 毫米狭缝重叠。</li>
		<li>使用数据采集软件记录氙质量谱。</li>
		<li>通过旋转 WP 角度来降低激光功率, 获得比先前测量的功率低20兆瓦的功率。</li>
		<li>重复步骤 3.1. 8-3. 1.9, 直到激光功率过低, 产生可测量的氙+信号。应记录在不同激光功率下的10-15 质谱。</li>
		<li>使用适当的数据分析软件, 按照参考28中的步骤, 识别氙+ (1.12 x 1014 W cm-2)28的绝对饱和强度对应的激光脉冲能量。本程序为进一步实验中使用的任何泵浦脉冲能量提供绝对强度刻度。</li>
	</ol></li>
	<li>探针脉冲绝对峰值强度的标定33 注: 由于探头脉冲强度较弱, 无法使用步骤3.1 中描述的氙标定方法。相反, 实验中的探针强度可以通过用数码相机32, 以及脉冲持续时间和能量来测量焦距的光斑大小来估计。<ol>
<li>用两个平镜在分色镜后, 堵住泵梁并沿直线方向引导探头束。</li>
		<li>从靠近腔室的位置移除聚焦透镜, 将其置于探头光束路径中, 以确保探头光束穿过其中心。</li>
		<li>使用可变钕滤波器将探头光束能量最小化, 并添加额外的 nd 滤波器以衰减100新泽西州以下的脉冲能量。</li>
		<li>将紧凑型 CMOS 相机放在手动的线性平移阶段, 并将其连接到具有适当数据采集软件的计算机上。在探头光束路径上装入平移阶段, 以靠近光束焦距的摄像机为中心。使用软件程序定位光束点。添加 ND 滤波器并调整相机采集设置, 以防止 CMOS 探测器的饱和。</li>
		<li>调整平移阶段的位置以获得最小、最强的激光光斑。这个位置对应于光束的焦点。</li>
		<li>在聚焦处获取相机图像, 并利用适当的数据分析软件确定光束直径, 使光斑适合于二维高斯函数。</li>
		<li>卸下将探头光束定向到照相机的镜像, 并将聚焦透镜返回到其在飞行前的位置。</li>
	</ol></li>
	<li>水泵探头空间和时间重叠的测定 注意: 假定在步骤3.1 中完成协议。虽然氙气体可以作为样本来确定空间和时间重叠, 建议使用目标分子进行研究, 因为质量频谱的变化可以观察到一系列的正时滞, 而不是只有在零时滞, 和氙气一样。<ol>
<li>将所需的样品连接到飞行室, 并将压力调整到 1-5 x 10-7乇的范围内。</li>
		<li>解除对泵和探头光束的解锁, 并确保它们与飞行时-MS 室对齐。</li>
		<li>通过调整 ND 滤波器, 使探头功率最大化。将泵浦功率与 waveplate 设置为足够高的电平以获得满意的离子信号。 注: 探头功率应足够高, 以诱导破碎, 但不太高, 以创造离子在没有泵浦脉冲。</li>
		<li>调整探头光束的空间位置, 在分色镜架上的旋钮 (DC,图 1), 直到所有离子强度的峰值被观察到 (如果舞台位置恰好是在零延迟) 或显著耗尽母体分子离子和/或增加片段离子产量被观察 (如果阶段位置对应于一个正时滞)。</li>
		<li>如果没有观察到离子信号的变化, 则阶段位置可能在负时滞, i., 探头在泵之前。将机动延迟阶段调整为探头光束的较长路径, 并重复步骤3.3.4 直到观察到质量谱的变化。</li>
		<li>调整机动延迟阶段位置, 产生总离子信号的峰值。此位置对应于零时间延迟。如图 3所示, 在零时滞时, 具有良好和较差的空间重叠的分子 DMMP 的代表性质谱, 以及仅采用泵束的质谱。</li>
	</ol></li>
	<li>交叉相关6,34 注: 交叉相关测量必须在惰性气体 (如氙32) 上进行。验证了用青蛙测量的脉冲持续时间和零时滞对应的延迟阶段位置。<ol>
<li>与氙气体在房间 (步骤 3.1) 和光束重叠优化 (步骤 3.3), 移动机动化的阶段位置定位零时滞 (i., 当氙+信号最大化)。</li>
		<li>将机动化的翻译阶段扫描-200 fs 至 +200 fs 的延迟范围, 步骤为 5 fs。此扫描对应于在零时间延迟位置以120µm 为中心的1.5 µm 的步骤。记录质量谱在每个扫描位置和集成氙+收益率获得时间依赖的离子信号34。</li>
	</ol></li>
</ol>4. 水泵探头测量
<ol><li>采取测量前的初步检查<ol>
<li>检查实验设置以确认两个光束通过腔室的窗口传播 collinearly (图 1)。</li>
		<li>将所需样品连接到飞行室, 并逐步将样品放入腔内, 使用可变的检漏阀, 以达到 1-5 x 10-7乇的靶压力。在调整采样压力时, 确保在时间上关闭 MS 电源电压, 以避免由于压力峰值而对 MCP 探测器造成损坏。</li>
		<li>如果分子的蒸气压过低, 无法产生所需的压力, 请轻轻加热试样保持器, 直到达到所需的压力。</li>
		<li>打开并检查 MS 电压 (步骤 3.1.5)。验证数据采集软件在与机动延时阶段和示波器的通信方面的可操作性。</li>
		<li>调整腔体前面的透镜 (步进 3.1.7) 和泵浦探头的空间对准 (步骤 3.3.4), 优化离子信号和空间重叠。</li>
	</ol>
</li>
	<li>数据采集<ol>
<li>调整泵和探头脉冲能量以获得所需的离子信号。</li>
		<li>在数据采集软件中, 指定扫描长度和步骤大小。 注: 我们实验的典型扫描长度范围从 1000-5000 fs 和步骤大小不等, 从 5-20 fs19,20。</li>
		<li>运行数据采集软件, 在每次泵探头延迟时获取质量频谱。 注: 通常情况下, 每次扫描时延迟记录的质量频谱平均为1000激光射击。为了获得足够高的信噪比, 10-20 扫描在所需的设置(i., 扫描长度, 步长, 泵和探头功率) 和平均值。为了尽量减少激光功率漂移的影响, 可以在延迟阶段旅行的交替方向进行扫描。所有数据都保存为制表符分隔的文本文件。如图 4所示, 以 5 fs 的步长为 1250年 fs 的扫描长度的单扫描 DMMP 中的代表性原始质量光谱数据。</li>
	</ol>
</li>
	<li>数据处理<ol>
<li>确定每个质量峰值的飞行时间范围 (图 4中括号内的区域所示), 并在每个质量谱中集成这些范围。输出表示每个感兴趣的时间分辨信号。例如, DMMP 母体分子离子的时间分辨离子信号具有良好的和较差的泵探针空间重叠, 从一个泵浦探针扫描, 如图 5所示。</li>
		<li>重复步骤4.3.1 以获得所需的扫描数量 (e., 10-20)19,20在相同的扫描设置。平均每个时间分辨离子信号在所有扫描采取。典型的平均离子信号如图 6所示。</li>
	</ol>
</li>
</ol>

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作者没有什么可透露的。

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?...

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。

<table><tbody><tr><td>&lt;strong&gt;Mass spectrometer components&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>TOF lens stack and flight tube assembly</td><td>Jordan TOF Products, Inc.</td><td>C-677</td><td></td></tr><tr><td>18 mm Z-gap detector assembly</td><td>Jordan TOF Products, Inc.</td><td>C-701Z</td><td></td></tr><tr><td>TOF high voltage power supply</td><td>Jordan TOF Products, Inc.</td><td>D-603</td><td></td></tr><tr><td>&lt;strong&gt;Vacuum system components&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Rotary vane backing pump</td><td>Edwards Vacuum LLC</td><td>RV12</td><td></td></tr><tr><td>Turbomolecular pumps (2)</td><td>Edwards Vacuum LLC</td><td>EXT255H</td><td></td></tr><tr><td>Turbomolecular pump controllers (2)</td><td>Edwards Vacuum LLC</td><td>EXC300</td><td></td></tr><tr><td>Pressure gauge</td><td>Edwards Vacuum LLC</td><td>AIGX-S-DN40CF</td><td></td></tr><tr><td>Chiller for water cooling</td><td>Neslab</td><td>CFT-25</td><td></td></tr><tr><td>&lt;strong&gt;Femtosecond laser system&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Ti:Sapphire regenerative amplifier</td><td>Coherent, Inc.</td><td>Astrella</td><td>oscillator and amplifier in a single integrated system</td></tr><tr><td>Optical Parametric Amplifer (OPA)</td><td>Light Conversion</td><td>TOPAS Prime</td><td></td></tr><tr><td>&lt;strong&gt;Motion control&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Motorized linear translation stage 1&quot; travel</td><td>Thorlabs</td><td>Z825B</td><td></td></tr><tr><td>controller for linear translation stage</td><td>Thorlabs</td><td>KDC 101</td><td></td></tr><tr><td>USB controller hub and power supply</td><td>Thorlabs</td><td>KCH 601</td><td></td></tr><tr><td>Manual linear translation stage 1&quot; travel</td><td>Thorlabs</td><td>PT1</td><td></td></tr><tr><td>&lt;strong&gt;Detectors&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Pyroelectric laser energy meter</td><td>Coherent, Inc.</td><td>1168337</td><td></td></tr><tr><td>Thermal laser power meter</td><td>Coherent, Inc.</td><td>5356E16R</td><td></td></tr><tr><td>Si-biased detector 200-1100 nm</td><td>Thorlabs</td><td>DET10A</td><td></td></tr><tr><td>Compact USB CMOS Camera</td><td>Thorlabs</td><td>DCC1545M</td><td></td></tr><tr><td>USB spectrometer</td><td>Ocean Optics</td><td>HR4000</td><td></td></tr><tr><td>1 GHz digital oscilloscope&amp;nbsp;</td><td>LeCroy</td><td>WaveRunner 610Zi</td><td></td></tr><tr><td>&lt;strong&gt;Optics&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Type 1 BBO crystal</td><td>Crylight Photonics</td><td>BBO007</td><td>aperture and thickness may be customized</td></tr><tr><td>Achromatic half wave plate, 1100-2000 nm</td><td>Thorlabs</td><td>AHWP05M-1600</td><td></td></tr><tr><td>Wollaston prism polarizer</td><td>Thorlabs</td><td>WPM10</td><td></td></tr><tr><td>Hollow retro-reflector</td><td>PLX, Inc.</td><td>OW-20-1C</td><td></td></tr><tr><td>Variable neutral density filter</td><td>Thorlabs</td><td>NDC-100C-2</td><td></td></tr><tr><td>Longpass dichroic mirror 2&quot; diameter</td><td>Thorlabs</td><td>DMLP950L</td><td></td></tr><tr><td>&lt;strong&gt;Software&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Digital Camera image software</td><td>Thorlabs</td><td>ThorCam</td><td></td></tr><tr><td>Instrument communication interface</td><td>National Instruments</td><td>NI-MAX</td><td></td></tr><tr><td>Graphical development environment for measurement programs</td><td>National Instruments</td><td>LabVIEW</td><td></td></tr><tr><td>Data processing software</td><td>Mathworks</td><td>MATLAB</td><td></td></tr></tbody></table>

measurement of ultrafast vibrational coherences in polyatomic radical cations with strong-field adiabatic ionization

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。

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?...

Watch this Scientific Journal Video about Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization at JoVE.com

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

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。

强场绝热电离多原子自由基阳离子超快振动相干的测量

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

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Chemistry

Chemical Bonding: Basic Concepts

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6.8K 次观看.  Virginia Commonwealth University. 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。

视频: Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

可调式真空紫外（VUV）同步辐射分子束质谱分析

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

科研

工程学

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 &#181;m spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO).
The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS.

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

Time-resolved atomic and diatomic molecular species are measured using LIBS. The spectra are collected at various time delays following the generation of optical breakdown plasma with Nd:YAG laser radiation&#160;and are analyzed to infer electron density and temperature.

测量和原子氢和双原子分子ALO，C分析<sub&gt; 2</sub&gt;，CN和二氧化钛光谱承接激光诱导光学击穿

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement ...

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With ~102-103 repetitions of the photoreaction, the minimum number to complete a scan at reasonable spectral resolution and bandwidth, the noise level in the absorption difference spectra can be as low as ~10-4, sufficient to follow the kinetics of protonation changes from a single amino acid. Lower noise levels can be accomplished by more data averaging and/or mathematical processing. The amount of protein required for optimal results is between 5-100 &#181;g, depending on the sampling technique used. Regarding additional requirements, the protein needs to be first concentrated in a low ionic strength buffer and then dried to form a film. The protein film is hydrated prior to the experiment, either with little droplets of water or under controlled atmospheric humidity. The attained hydration level (g of water / g of protein) is gauged from an IR absorption spectrum. To showcase the technique, we studied the photocycle of the light-driven proton-pump bacteriorhodopsin in its native purple membrane environment, and of the light-gated ion channel channelrhodopsin-2 solubilized in detergent.

Key steps of protein function, in particular backbone conformational changes and proton transfer reactions, often take place in the microsecond to millisecond time scale. These dynamical processes can be studied by time-resolved step-scan Fourier-transform infrared spectroscopy, in particular for proteins whose function is triggered by light.

质子转移和蛋白质构象动力学的光敏蛋白的时间分辨步进扫描傅立叶变换红外光谱

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards ...

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

激光驱动的超快分子旋转直接成像

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

化学

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish between enantiomers (stereoisomers) of simple chiral species on the level of individual molecules. In this approach, a gaseous molecular jet of the sample expands into a vacuum chamber and intersects with femtosecond (fs) laser pulses. The high intensity of the pulses leads to fast multiple ionization, igniting a so-called Coulomb Explosion that produces several cationic (positively charged) fragments. An electrostatic field guides these cations onto time- and position-sensitive detectors. Similar to a time-of-flight mass spectrometer, the arrival time of each ion yields information on its mass. As a surplus, the electrostatic field is adjusted in a way that the emission direction and the kinetic energy after fragmentation lead to variations in the time-of-flight and in the impact position on the detector.
Each ion impact creates an electronic signal in the detector; this signal is treated by high-frequency electronics and recorded event by event by a computer. The registered data correspond to the impact times and positions. With these data, the energy and the emission direction of each fragment can be calculated. These values are related to structural properties of the molecule under investigation, i.e. to the bond lengths and relative positions of the atoms, allowing to determine molecule by molecule the handedness of simple chiral species and other isomeric features.

For small chiral species, Coulomb Explosion Imaging provides a new approach to determine the handedness of individual molecules.

作为一种工具来区分立体异构体的库仑爆炸成像

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish ...

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered &#39;random&#39;. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

We describe an experiment designed to probe the electronic damage induced in nanocrystals of Buckminsterfullerene (C60) by intense, femtosecond pulses of X-rays. The experiment found that, surprisingly, rather than being stochastic, the X-ray induced electron dynamics in C60 are highly correlated, extending over hundreds of unit cells within the crystals1.

在纳米富勒的飞秒衍射实验的长程电子关联的测量

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the ...

An Experimental Protocol for Femtosecond NIR/UV - XUV Pump-Probe Experiments with Free-Electron Lasers

This protocol describes key steps in performing and analyzing femtosecond pump-probe experiments that combine a femtosecond optical laser with a free-electron laser. This includes methods to establish the spatial and temporal overlap between the optical and free-electron laser pulses during the experiment, as well as important aspects of the data analysis, such as corrections for arrival time jitter, which are necessary to obtain high-quality pump-probe data sets with the best possible temporal resolution. These methods are demonstrated for an exemplary experiment performed at the FLASH (Free-electron LASer Hamburg) free-electron laser in order to study ultrafast photochemistry in gas-phase molecules by means of velocity map ion imaging. However, most of the strategies are also applicable to similar pump-probe experiments using other targets or other experimental techniques.

This protocol describes the key steps for performing and analyzing pump-probe experiments combining a femtosecond optical laser with a free-electron laser in order to study ultrafast photochemical reactions in gas-phase molecules.

用自由电子激光器进行飞秒近红外/紫外 XUV 泵-探针实验的实验协议

This protocol describes key steps in performing and analyzing femtosecond pump-probe experiments that combine a femtosecond optical laser with a ...

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F&#8722;

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F&#8722;), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.

Here, we present a protocol for photoelectron imaging of anionic species. Anions generated in vacuo and separated by mass spectrometry are probed using velocity mapped photoelectron imaging, providing details of anion and neutral energy levels, anion and neutral structure and the nature of the anion electronic state.

由 F− 310 Nm 支队所示的阴离子光电子成像

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

超快时间解析近红外刺激拉曼测量功能 +偶联系统

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

The accurate molecular simulation prediction of vibrational spectra, and other structural, energetic and spectral characteristics, of photo-active metal-oxide surfaces in contact with light-absorbing dyes is an ongoing thorny and elusive challenge in physical chemistry. With this in mind, a molecular-dynamics (MD) simulation were performed by using optimized empirical potentials for a well-representative and prototypical dye-sensitized solar cell (DSC) solvated by a widely-studied room temperature ionic liquid (RTIL), in the guise of a [bmim]+[NTf2]- RTIL solvating an N719-sensitizing dye adsorbed onto 101 anatase-titania. In doing so, important insights were gleaned into how using a RTIL as the electrolytic hole acceptor modulates the dynamical and vibrational properties of a N719 dye, estimating the spectra for the DSC photo-active interface via Fourier transformation of mass-weighted velocity autocorrelation functions from MD. The acquired vibrational spectra were compared with the experiment spectra and those sampled from ab initio molecular dynamics (AIMD); in particular, various empirical-potential spectra generated from MD provide insight into how partial-charge charge parameterization of the ionic liquid affects vibrational spectra prediction. In any event, careful fitting of empirical force-field models has been shown to be an effective tool in handling DSC vibrational properties, when validated by AIMD and an experiment.

A dye-sensitized solar cell was solvated by RTILs; using optimized empirical potentials, a molecular dynamics simulation was applied to compute vibrational properties. The obtained vibrational spectra were compared with experiment and ab initio molecular dynamics; various empirical potential spectra show how partial-charge charge parameterization of the ionic liquid affects vibrational spectra prediction.

强场绝热电离多原子自由基阳离子超快振动相干的测量

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