I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
Environmental Molecular Science Group, EMTech, AIST Tsukuba West, Onogawa 16-1, Tsukuba, Ibaraki 305-8569, Japan.
Science. 2015 Mar 20;347(6228):1346-9. doi: 10.1126/science.aaa3304.
Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5(+), a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5(+) samples poses a formidable challenge. By applying two types of action spectroscopy predicated on photoinduced reaction with CO2 and photoinhibition of helium cluster growth, we obtained low-temperature, high-resolution spectra of mass-selected CH5(+). On the basis of the very high accuracy of the line positions, we determined a spectrum of combination differences. Analysis of this spectrum enabled derivation of equally accurate ground state-level schemes of the corresponding nuclear spin isomers of CH5(+), as well as tentative quantum number assignment of this enfant terrible of molecular spectroscopy.
质子化甲烷（CH4）是一个相当刚性的分子，可通过量子力学很好地描述，其产物 CH5(+) 是一个典型的柔软分子，一直未能被明确的光谱描述。实验测量纯 CH5(+)样品的高分辨率光谱具有很大的挑战性。通过应用两种基于与 CO2 光诱导反应和氦团簇生长光抑制的作用光谱，我们获得了质量选择的 CH5(+)的低温、高分辨率光谱。基于线位置的极高精度，我们确定了组合差的光谱。对该光谱的分析使得能够推导出 CH5(+)的相应核自旋异构体的同样精确的基态能级方案，以及对分子光谱这个可怕婴儿的量子数分配的试探性确定。
