Understanding the Infrared Spectrum of Bare CH5+
Understanding the Infrared Spectrum of Bare CH5+
复制标题
了解裸 CH5 的红外光谱
作者：
O. Asvany;P. P;B. Redlich;Ilka Hegemann;S. Schlemmer;D. Marx
质子化甲烷（CH5+）仍然无法确定其结构归属，因为大振幅振动和氢扰对理论和实验都提出了挑战。图中是在荷兰FELIX装置中，由自由电子激光共振激发后与二氧化碳气体反应所检测到的裸CH5+的红外光谱。通过从头算分子动力学计算，将~ 110开尔文的实验光谱与有限温度红外光谱进行比较，支持了实验条件下裸CH5+的流动性，并提供了CH3三脚架位置和三中心键合H2部分之间氢交换的动力学机制，最终导致全氢乱序。在模拟中，人为冻结干扰和内部旋转的可能性允许分配红外光谱，尽管这种明显的流动性。
Protonated methane, CH5+, continues to elude definitive structural assignment, as large-amplitude vibrations and hydrogen scrambling challenge both theory and experiment. Here, the infrared spectrum of bare CH5+ is presented, as detected by reaction with carbon dioxide gas after resonant excitation by the free electron laser at the FELIX facility in the Netherlands. Comparison of the experimental spectrum at ∼110 kelvin to finite-temperature infrared spectra, calculated by ab initio molecular dynamics, supports fluxionality of bare CH5+ under experimental conditions and provides a dynamical mechanism for exchange of hydrogens between CH3 tripod positions and the three-center bonded H2 moiety, which eventually leads to full hydrogen scrambling. The possibility of artificially freezing out scrambling and internal rotation in the simulations allowed assignment of the infrared spectrum despite this pronounced fluxionality.