High Resolution Spectroscopy of protonated methane: Structure and dynamics of floppy molecules

本项目的重点是神秘的CH5+分子离子的光谱。它是一种结合强烈但流动性很强的分子的原型。因此，对于CH5+和类似的分子，用球棒图表示的分子结构的总体图景是有问题的。在第一个资助期，非常高分辨率的红外光谱显示了最低能量状态的能量项图的第一视图。我们成功地将该分子的三个不同核自旋态的跃迁与五个等价的质子联系在一起。这是指认这种非常规分子光谱的第一步。根据该项目在过去六年中的实验进展，将有可能记录CH5+的太赫兹光谱，从而找到最低的能量跃迁，它们可能是纯旋转或无振动的性质。我们的实验发展得到了对分子能量项及其跃迁的强大的、新的理论描述的补充。这种完全不同的方法是由最近的一项发现触发的，即无振动波函数不再可以分为旋转和振动部分。取而代之的是，部分来自核物理的新模型将揭示传统扭曲刚性转子方法之外的术语图。在这个实验和理论相结合的项目中，测量和解释CH5+的光谱可能会导致对非刚性分子从弱结合团簇到更强结合结构的全面、恰当的描述。因此，该项目的目标是从根本上提高对分子物理学的理解。

This project focuses on the spectroscopy of the enigmatic CH5+ molecular ion. It is the prototype of a strongly bound yet very fluxional molecule. As a result the general picture of a molecular structure represented by a ball and stick diagram is in question for CH5+ and similar molecules. In the first funding period infrared spectra at very high resolution have revealed a first view at the energy term diagram of the lowest energy states. We succeeded to associate transitions to the three distinct nuclear spin states of this molecule with five equivalent protons. This is the first step in assigning the spectrumof this unconventional molecule. Based on the experimental developments in this project in the last six years it will be possible to record the THz spectrum of CH5+ and thus to find the lowest energy transitions, may they be pure rotational or ro-vibrational in nature. Our experimental development is complemented by a powerful, new theoretical description of the molecular energy terms and their transitions. This fundamentally different approach is triggered by the recent finding that the ro-vibrational wave-function no longer can be separated into a rotational and vibrational part. Instead the new model, partly adoptedfrom nuclear physics will reveal term diagrams beyond the traditional distorted rigid rotor approach. Measuring and interpreting the spectrum of CH5+ in this combined experimental and theoretical project potentially will lead to a general, proper description of non-rigid molecules from weakly bound clusters to more strongly bound structures. Therefore the project aims at fundamentally improved understanding of molecular physics.