Spectroscopic Studies of Large-Amplitude Motions in Methyl-Rotor-Containing Molecules Important to Fundamental Physics, Astronomy and Chemical Dynamics

含甲基转子分子大振幅运动的光谱研究对基础物理、天文学和化学动力学很重要

• 批准号: RGPIN-2017-03817
• 负责人: Xu, LiHong
• 金额: $ 2.62万
• 依托单位: University of New Brunswick
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=669087
• 关键词: Spectroscopic; Studies; Large; Amplitude; Motions

Summary of Proposal******The primary focus of this NSERC Discovery Grant application is on precision spectroscopy and characterization of complex organic gas-phase molecules of fundamental and practical importance. Molecules being investigated are (i) internal-rotor-containing species known to have enhanced sensitivity for probing variation of fundamental constants and known to promote torsion-mediated vibrational energy redistribution; and (ii) sulphur-containing molecules for which data are urgently needed by the astronomical community in order to understand sulphur chemistry and the “missing Sulphur” question in dense molecular clouds.****Future work will build on our past success and extend it in the following directions:****(1) Torsion-enhanced hyperfine splittings in methyl-rotor species. We have successfully modeled unexpected and previously unseen hyperfine doublets in methanol that arise from a totally new torsionally-mediated methyl proton spin-rotation effect, a unique combination of large-amplitude torsional motion with proton spin and overall rotation. This raises interesting questions that we will address: (i) does this torsionally-mediated effect exist in other methyl-rotor molecules; (ii) can we develop analytical tools to predict and model these splittings for a wide range of species; (iii) is this enhanced effect related to the torsional parameter ρ (ratio of moment of inertia of the top to that of the whole molecule); and (iv) what are the implications of these splittings for astronomical findings?****(2) Sulphur chemistry in the interstellar medium is not well understood. This problem is important as sulphur-bearing molecules are used to probe the physical structure of star-forming regions and have been proposed as chemical clocks to obtain information about the age of hot cores from a knowledge of their physical conditions. However, significantly less sulphur is found in dense regions of the ISM than in diffuse regions, creating the “missing Sulphur problem”. We will target benchmark laboratory databases needed for sulphur-containing compounds to assist understanding of the missing sulphur question in dense molecular clouds.****(3) High-resolution spectra have revealed complicated networks of interactions in all vibrational modes of methanol all the way up to the 3 μm region, Methyl mercaptan and isotopic variants of methanol show close similarities but also dramatic contrasts. The observed torsional patterns in the excited vibrational states deviate significantly from that in the ground state, ranging from reduced torsional splittings to completely inverted torsional patterns. Our findings call for a new way of treating large-amplitude motion when vibrations are excited. The combination of experimental observations and ab initio molecular modeling will lead to new insights into the complex nature of the torsion-vibration coupling and dynamics.**

提案摘要 ** NSERC发现资助申请的主要重点是具有基础和实际重要性的复杂有机气相分子的精密光谱学和表征。正在研究的分子是：（一）已知对探测基本常数的变化具有增强的灵敏度并已知促进扭转介导的振动能量重新分布的含有内转子的物质;和（二）天文学界迫切需要其数据的含硫分子，以便了解硫化学和致密分子云中的“失踪硫”问题。未来的工作将建立在我们过去的成功，并扩大它在以下方向：****（1）扭转增强超精细分裂甲基转子物种。我们已经成功地模拟了意外的和以前看不见的超精细双峰在甲醇中产生的一个全新的扭转介导的甲基质子自旋旋转效应，大幅度扭转运动与质子自旋和整体旋转的独特组合。这提出了有趣的问题，我们将解决：（i）这种扭转介导的影响是否存在于其他甲基转子分子;（ii）我们能否开发分析工具来预测和模拟这些分裂的广泛物种;（iii）这种增强效应是否与扭转参数ρ有关（顶部的惯性矩与整个分子的惯性矩之比）;以及（iv）这些分裂对天文学发现的影响是什么？* (2)星际介质中的硫化学还没有得到很好的理解。这个问题很重要，因为含硫分子被用来探测恒星形成区域的物理结构，并被提议作为化学钟，从其物理条件的知识中获得有关热核年龄的信息。然而，在ISM的密集区域中发现的硫明显少于扩散区域，从而产生了“硫缺失问题”。我们将针对含硫化合物所需的基准实验室数据库，以帮助理解致密分子云中缺少硫的问题。(3)高分辨率光谱揭示了甲醇所有振动模式中复杂的相互作用网络，一直到3 μm区域，甲硫醇和甲醇的同位素变体表现出密切的相似性，但也存在显着的对比。在激发振动状态下观察到的扭转模式偏离显着从基态，从减少扭转分裂完全反转的扭转模式。我们的研究结果要求一种新的方法来处理大振幅运动时，振动激发。实验观察和从头算分子建模的结合将导致对扭转振动耦合和动力学的复杂性质的新见解。