Assessing the Impact of Tagging Species on the Fluxional Behavior of Protonated Methane

质子化甲烷被认为是一种典型的流动分子，因为明显的大振幅运动导致所谓的氢乱序。鉴于这种非经典碳正离子母体的基本重要性，几十年来人们一直在对其进行深入研究。然而，基本上尚未探索的是假定的相互作用引起的大振幅运动的扰动和由于附加弱相互作用的光物种而引起的混乱，这是本项目的唯一焦点。事实上，质子化的甲烷已经用氢分子标记在先驱信使作用光谱学的工作中。此外，氦原子是另一种理想的标记物种，已广泛用于其他分子，特别是准刚性分子。该项目有两个不同的组件，通过使用最近开发的两种不同的从头计算路径积分技术来实现。第一个重点是100 K至低频波段的宽带红外光谱的近似计算，以阐明质子化甲烷与少量氢分子的振动光谱相互作用。第二个重点是在少量氦- 4原子的影响下，结合玻色-爱因斯坦统计对质子化甲烷分子结构在1k左右的温度下的振幅运动和乱序的影响。

Protonated methane is considered to be an archetypal fluxional molecule since pronounced large-amplitude motion leads to so-called hydrogen scrambling. Given the fundamental importance of this parent of non-classical carbocations, it has been intensely studied since decades. What remains essentially unexplored, however, are the putative interaction-induced perturbations of large-amplitude motion and scrambling due to attaching weakly interacting light species, which is the exclusive focus of this project. Indeed, protonated methane has been tagged using hydrogen molecules in pioneering messenger action spectroscopy work of Y. T. Lee. Moreover, helium atoms are another ideal tagging species that has been widely used for other molecules, in particular quasi-rigid ones. This project has two different components which are enabled by using two distinct ab initio path integral-based techniques as developed recently. The first focus is the approximate computation of broadband infrared spectra at temperatures on the order of 100 K down to the region of low frequencies to elucidate the interactions of protonated methane with a few hydrogen molecules in terms of vibrational spectroscopy. The second focus is on the impact of only a few helium-four atoms in conjunction with Bose-Einstein statistics on large-amplitude motion and scrambling of protonated methane at temperatures on the order of 1 K in terms of its molecular structure.