Infrared and Raman Spectroscopic Study of Methane Clathrate Hydrates at Low Temperatures and High Pressures: Dynamics and Cage Occupancy of Methane
Infrared and Raman Spectroscopic Study of Methane Clathrate Hydrates at Low Temperatures and High Pressures: Dynamics and Cage Occupancy of Methane
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低温高压下甲烷笼形水合物的红外和拉曼光谱研究：甲烷的动力学和笼占有率
DOI：
10.1021/acs.jpcc.0c09315
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Okamura Hidekazu
中科院分区：
文献类型：
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作者：
Noguchi Naoki;Yonezawa Takuya;Yokoi Yuu;Tokunaga Tomoki;Moriwaki Taro;Ikemoto Yuka;Okamura Hidekazu
在低温高压条件下测量了甲烷水合物（MH）的红外（IR）吸收光谱和拉曼光谱，研究了甲烷水合物中CH 4分子的动力学、笼位以及I（MH-I）、II（MH-II）和III（MH-III）相的水合数.在40 K以下，MH-I的红外光谱在M（51262）笼中CH_4分子不对称伸缩（ν3）模的波数区出现了归属于振转跃迁的谱带。这是CH 4的准转子行为的证据。在1.3GPa以下和40 K以下的红外光谱中也观察到了MH-II的振转谱带。有趣的是，在1.3GPa以上，MH-Ⅱ的拉曼和红外光谱中的完全对称伸缩（ν1）和ν 3带的形状发生了显著变化。这表明LL（51268）笼的笼占有率在1.3 GPa下通过脱水从1变为2。在1.3GPa下，水化数由5.38 ± 0.05变为4.80 ± 0.17。LL笼中的双占据态可能是由CH 4分子的二聚体形成引起的。
Infrared (IR) absorption and Raman spectra of methane hydrate (MH) were measured at low temperatures and high pressures to reveal the dynamics and cage occupancy of CH4molecules and the hydration numbers in phases I (MH-I), II (MH-II), and III (MH-III). For the IR spectra of MH-I below 40 K, bands assigned to the rovibrational transition appeared in the wavenumber region of the asymmetric stretching (ν3) mode of CH4molecules in the M (51262) cages. This is evidence of the quasi-rotor behavior of CH4. The rovibrational bands were also observed in the IR spectra of MH-II below 1.3 GPa and below 40 K. Interestingly, the shapes of the totally symmetric stretching (ν1) and ν3bands in the Raman and IR spectra of MH-II changed drastically above 1.3 GPa. This suggests that the cage occupancy of the LL (51268) cage changed from one to two via dehydration at 1.3 GPa. The hydration number also changed from 5.38 ± 0.05 to 4.80 ± 0.17 at 1.3 GPa. A doubly occupied state in the LL cage may arise from the formation of a dimer of CH4molecules.