Mid-Infrared Frequency Comb Lasers for Chemical Kinetics: Applying Physics Technologies to Kinetics, Dynamics, and Molecular Spectroscopy

用于化学动力学的中红外频率梳状激光器：将物理技术应用于动力学、动力学和分子光谱学

• 批准号: EP/R01518X/1
• 负责人: Julia Lehman
• 金额: $ 8.69万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FR01518X%2F1
• 关键词: Mid; Infrared; Frequency; Comb; Lasers

A simple chemical reaction could be described as an interaction between two reactant molecules, A + B, which leads to the formation of two new product molecules, C + D. This process involves the breaking and making of chemical bonds, giving the products inherently different properties than the reactants. One way to identify the product and reactant molecules is by using vibrational spectroscopy. Each bond in a molecule vibrates at a specific frequency, making the vibrational absorption spectrum of one molecule (such as molecule A) different than another molecule (such as molecules B, C, or D), like a "fingerprint" identifying that molecule. However, because bonds in different molecules could vibrate at vastly different frequencies, it is hard to view the fingerprints of all of the molecules in the A + B -> C + D reaction at once. To do so, a simultaneously broadband and high resolution vibrational absorption spectrum would be needed. However, it would also be useful to know the timescale for the reaction. Suppose further that this reaction was competing with another reaction, like A + B -> E. It is then not only important to know the rate at which molecules A and B disappeared, but also the rate at which C, D, and E appeared. From the above hypothetical chemical reactions, we realize that it is important to know both the identity of molecules involved in a reaction (reactants and products) as well as the rate at which they disappear or appear. Thus, it is essential to use a simultaneously broadband (wide spectral width) and high spectral resolution technique, combined with the time resolution necessary to monitor the kinetics of the chemical reactions. The proposed research uses a technique developed by the optical physics community called cavity-enhanced direct frequency comb spectroscopy and applies it to a fundamentally interesting radical-radical reaction. Here, a frequency comb laser is the source of the infrared radiation necessary to excite molecular vibrations. It is a broadband source, so it can excite a range of different molecular vibrations within a wide spectral region (3 - 3.5 microns). It is unique, though, in that thousands of spectrally narrow "comb teeth" make up this broadband source, each with a known and controllable frequency. This makes it both broadband and high resolution, meeting the criteria for being able to spectrally identify molecules based on their vibrational fingerprints. This light source is passed through a reaction cell, where a chemical reaction takes place (in the proposed experiment, the initial target reaction is the radical-radical reaction CH2SH + NO). Some of the molecules involved in this reaction absorb the infrared radiation, attenuating the amount of infrared light passing through the reaction cell at the specific frequencies ("comb teeth") that the molecules absorbed. In the proposed research, the "comb teeth" of this light source are spatially dispersed onto an infrared sensitive camera, giving a high resolution vibrational absorption spectrum of what is contained in the gas cell. The camera takes images as the reaction occurs, yielding vibrational absorption spectra as a function of reaction time, thus simultaneously identifying and mapping the timescale of the appearance (and disappearance) of molecules involved in the chemical reaction. This is a unique technique to be applied to studying the kinetics and dynamics of chemical reactions, where a significant amount of detail about a chemical reaction is contained in this high resolution, time-resolved spectrum.

一个简单的化学反应可以描述为两个反应物分子A + B之间的相互作用，这导致两个新的产物分子C + D的形成。这个过程涉及化学键的断裂和形成，使产物具有与反应物不同的性质。识别产物和反应物分子的一种方法是使用振动光谱。分子中的每个键都以特定的频率振动，使得一个分子（如分子A）的振动吸收光谱不同于另一个分子（如分子B、C或D），就像识别该分子的“指纹”。然而，由于不同分子中的键可能以截然不同的频率振动，因此很难同时查看A + B -> C + D反应中所有分子的指纹。为此，需要同时具有宽带和高分辨率的振动吸收光谱。然而，了解反应的时间表也是有用的。进一步假设这个反应与另一个反应竞争，如A + B -> E。因此，不仅要知道分子A和B消失的速率，还要知道C、D和E出现的速率。从上述假设的化学反应中，我们认识到，知道反应中所涉及的分子（反应物和产物）的身份以及它们消失或出现的速率是很重要的。因此，必须同时使用宽带（宽光谱宽度）和高光谱分辨率技术，并结合监测化学反应动力学所需的时间分辨率。这项拟议中的研究使用了一种由光学物理界开发的技术，称为腔增强直接频率梳状光谱，并将其应用于一个从根本上有趣的自由基-自由基反应。这里，频率梳状激光器是激发分子振动所需的红外辐射源。它是一个宽带源，因此它可以在宽光谱范围（3 - 3.5微米）内激发一系列不同的分子振动。然而，它的独特之处在于，数千个光谱狭窄的“梳齿”组成了这个宽带源，每个梳齿都有一个已知的和可控的频率。这使得它具有宽带和高分辨率，满足能够根据振动指纹光谱识别分子的标准。该光源穿过反应池，在反应池中发生化学反应（在所提出的实验中，初始目标反应是自由基-自由基反应CH 2SH + NO）。参与该反应的一些分子吸收红外辐射，衰减以分子吸收的特定频率（“梳齿”）通过反应池的红外光的量。在拟议的研究中，这种光源的“梳齿”在空间上分散到红外敏感相机上，给出了气室中所含物质的高分辨率振动吸收光谱。相机在反应发生时拍摄图像，产生作为反应时间函数的振动吸收光谱，从而同时识别和绘制化学反应中所涉及的分子出现（和消失）的时间尺度。这是一种独特的技术，可应用于研究化学反应的动力学和动力学，其中关于化学反应的大量细节包含在这种高分辨率，时间分辨光谱中。

项目成果

Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH 2 Br 2 in the 2960 to 3120 cm -1 region

基于光学频率梳的测量和CH 2 Br 2 2960至3120 cm -1 区域高分辨率光谱的重新分配

• DOI: 10.1039/d2cp05881b
• 发表时间: 2023
• 期刊: Physical Chemistry Chemical Physics
• 影响因子: 3.3
• 作者: Sadiek I

A rapid, spatially dispersive frequency comb spectrograph aimed at gas phase chemical reaction kinetics

• DOI: 10.1080/00268976.2020.1733116
• 发表时间: 2020-02-27
• 期刊: MOLECULAR PHYSICS
• 影响因子: 1.7
• 作者: Roberts, Frances C.;Lewandowski, H. J.;Lehman, Julia H.
• 通讯作者: Lehman, Julia H.

Infrared frequency comb spectroscopy of CH2I2: Influence of hot bands and pressure broadening on the ?1 and ?6 fundamental transitions.

CH2I2 的红外频率梳光谱：热带和压力展宽对 ?1 和 ?6 基本跃迁的影响。

• DOI: 10.1063/5.0081836
• 发表时间: 2022
• 期刊: The Journal of chemical physics
• 作者: Roberts FC