Department of Chemistry, The University of Akron, Akron, Ohio 44325, USA.
J Phys Chem A. 2011 Sep 1;115(34):9748-63. doi: 10.1021/jp202020u. Epub 2011 Jun 13.
Infrared spectra of jet-cooled CH(3)OD and CH(3)OH in the CH stretch region are observed by coherence-converted population transfer Fourier transform microwave-infrared (CCPT-FTMW-IR) spectroscopy (E torsional species only) and by slit-jet single resonance spectroscopy (both A and E torsional species, CH(3)OH only). Twagirayezu et al. reported the analysis of ν(3) symmetric CH stretch region (2750-2900 cm(-1); Twagirayezu et al. J. Phys. Chem. A 2010, 114, 6818), and the present work addresses the more complicated higher frequency region (2900-3020 cm(-1)) containing the two asymmetric CH stretches (ν(2) and ν(9)). The additional complications include a higher density of coupled states, more extensive mixing, and evidence for Coriolis as well as anharmonic coupling. The overall observed spectra contain 17 interacting vibrational bands for CH(3)OD and 28 for CH(3)OH. The sign and magnitude of the torsional tunneling splittings are deduced for three CH stretch fundamentals (ν(3), ν(2), ν(9)) of both molecules and are compared to a model calculation and to ab initio theory. The number and distribution of observed vibrational bands indicate that the CH stretch bright states couple first to doorway states that are binary combinations of bending modes. In the parts of the spectrum where doorway states are present, the observed density of coupled states is comparable to the total density of vibrational states in the molecule, but where there are no doorway states, only the CH stretch fundamentals are observed. Above 2900 cm(-1), the available doorway states are CH bending states, but below, the doorway states also involve OH bending. A time-dependent interpretation of the present FTMW-IR spectra indicates a fast (∼200 fs) initial decay of the bright state followed by a second, slower redistribution (about 1-3 ps). The qualitative agreement of the present data with the time-dependent experiments of Iwaki and Dlott provides further support for the similarity of the fastest vibrational relaxation processes in the liquid and gas phases.
本文报道了用相干转换布居转移傅里叶变换微波-红外光谱（仅 E 扭态势）和狭缝喷射单共振光谱（A 和 E 扭态势，仅 CH3OH）观察到的处于 CH 伸缩区域的射流冷却的 CH3OD 和 CH3OH 的红外光谱。Twagirayezu 等人曾报道过 ν3对称 CH 伸缩区域（2750-2900 cm-1；Twagirayezu 等人，J. Phys. Chem. A，2010，114，6818）的分析，而本工作则涉及更为复杂的高频区域（2900-3020 cm-1），其中包含两个不对称的 CH 伸缩（ν2和 ν9）。附加的复杂性包括耦合态密度更高、混合程度更高、以及科里奥利力和非谐耦合的证据。观察到的光谱整体包含 17 个相互作用的 CH3OD 振动带和 28 个 CH3OH 振动带。两种分子的三个 CH 伸缩基频（ν3、ν2、ν9）的扭转隧道分裂的符号和大小被推断出来，并与模型计算和从头计算理论进行了比较。观察到的振动带的数量和分布表明，CH 伸缩亮态首先与弯曲模式的二进制组合的 doorway 态耦合。在 doorway 态存在的光谱部分中，观察到的耦合态密度与分子中振动态的总密度相当，但在没有 doorway 态的情况下，仅观察到 CH 伸缩基频。在 2900 cm-1以上，可用的 doorway 态是 CH 弯曲态，但在以下情况下， doorway 态也涉及 OH 弯曲。对本 FTMW-IR 光谱的时变解释表明，亮态的初始衰减很快（约 200 fs），随后是第二较慢的重新分布（约 1-3 ps）。本数据与 Iwaki 和 Dlott 的时变实验的定性一致性为液体和气相中最快的振动弛豫过程的相似性提供了进一步的支持。
