OH/OD Isotopic Shift Factors of Isolated and H-Bonded Surface Silanol Groups
OH/OD Isotopic Shift Factors of Isolated and H-Bonded Surface Silanol Groups
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DOI：
10.1021/jp400106s
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发表时间：
2013-03-14
影响因子：
3.7
通讯作者：
Hadjiivanov, Konstantin
中科院分区：
文献类型：
--
作者：
Chakarova, Kristina;Drenchev, Nikola;Hadjiivanov, Konstantin
SiO_2和[Si]_2上的OH/OD同位素位移因子（i = nu（OH）/nu（OD））在1.3563 ~ 1.3568之间，低于理论位移值1.3744。然而，谐波OH模的i值与理论值几乎一致，这表明在这种情况下的实验偏差主要是由于非谐性。当OH基团与吸附的CH 4或CO形成弱氢键时，非谐性略有降低，这将导致i增加。然而，与这些期望相反，i进一步减小。这归因于与相应的OH相比，OD基团的酸度较低。与分离的SiOH基团相比，H-键合的硅烷醇的i值也较低。它的结论是，i取决于H-键合的程度，它允许容易区分孤立和H-键合的表面羟基。
The OH/OD isotopic shift factors (i = nu(OH)/nu(OD)) of isolated silanols on SiO2 and [Si]BEA are between 1 3563 and 1.3568, values lower than the theoretical shift of 1.3744. However, i of the harmonic OH modes almost coincides with the theoretical value which indicates that the experimental deviations in this case are mainly due to anharmonicity. The anharmonicity slightly decreases when the OH groups participate in weak H-bonding with adsorbed CH4 or CO which should lead to an increase of i. However, contrary to these expectations, i additionally decreases. This is attributed to the lower acidity of the OD groups as compared to the respective OHs. The value of i is also lower for H-bonded silanols as compared to isolated SiOH groups. It is concluded that i depends on the extent of H-bonding which allows easy distinguishing between isolated and H-bonded surface hydroxyls.