Miller Isaac, Faulkner Ty, Raston Paul L
Department of Chemistry and Biochemistry , James Madison University , Harrisonburg , Virginia 22807 , United States.
Department of Chemistry , University of Adelaide , Adelaide , SA 5005 , Australia.
J Phys Chem A. 2019 Feb 28;123(8):1630-1636. doi: 10.1021/acs.jpca.8b12576. Epub 2019 Feb 13.
High-resolution, mid-infrared spectra of methanol isotopologues (CHOH, CHOD, CDOH, and CDOD) embedded in superfluid helium nanodroplets have been obtained. For the normal isotopologue, we observed the CO stretching overtone band, the lines within which are 2× broader than in the fundamental for E species methanol and no different than the fundamental for A species methanol. For CHOD, we observed the CO stretching overtone band for the first time, which was characterized by narrow line widths for both nuclear spin species. Spectra in the CD stretching bands were much broader, which is attributed to rapid relaxation to nearby anharmonically coupled vibrational state(s). Apparently the coupling is much stronger for CDOD, for which the rotational substructure is completely washed out. Inertial analyses of the rotationally resolved fundamental and overtone bands reveal that the moment of inertia of helium, Δ I, that couples to rotation decreases in going from the heavier (CDOH) to lighter (CHOH) isotopologues (i.e., with decreasing gas phase moment of inertia, I). The dependence of Δ I on I is larger than that found for other molecules in regions approaching the heavy and light rotor limits, which suggests a relatively large breakdown in the adiabatic following of helium density for this moderately light rotor.
已获得嵌入超流氦纳米液滴中的甲醇同位素分子（CH₃OH、CH₃OD、CD₃OH和CD₃OD）的高分辨率中红外光谱。对于正常同位素分子，我们观察到了C=O伸缩泛频带，其中的谱线比E类甲醇基频带中的谱线宽两倍，且与A类甲醇基频带中的谱线无异。对于CH₃OD，我们首次观察到了C=O伸缩泛频带，其特征是两种核自旋物种的谱线宽度都很窄。CD伸缩带中的光谱要宽得多，这归因于快速弛豫到附近非谐耦合振动态。显然，对于CD₃OD，这种耦合要强得多，其转动亚结构完全消失。对转动分辨的基频带和泛频带的惯性分析表明，与转动耦合的氦的转动惯量ΔI，在从重（CD₃OH）到轻（CH₃OH）的同位素分子中减小（即随着气相转动惯量I减小）。在接近重转子和轻转子极限的区域，ΔI对I的依赖性比其他分子的情况更大，这表明对于这个中等轻的转子，氦密度的绝热跟随存在相对较大的破坏。
