EXPERIMENTAL AND SIMULATED VIBRATIONAL-SPECTRA OF H-2 ABSORBED IN AMORPHOUS ICE - SURFACE-STRUCTURES, ENERGETICS, AND RELAXATIONS
EXPERIMENTAL AND SIMULATED VIBRATIONAL-SPECTRA OF H-2 ABSORBED IN AMORPHOUS ICE - SURFACE-STRUCTURES, ENERGETICS, AND RELAXATIONS
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DOI：
10.1063/1.463240
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发表时间：
1992-07-15
影响因子：
4.4
通讯作者：
BUCH, V
中科院分区：
文献类型：
--
作者：
HIXSON, HG;WOJCIK, MJ;BUCH, V
报道了在12K下形成的、被吸附分子氢饱和的氚化微孔无定形冰薄膜的红外光谱。本文着重研究了表面结合H-2对悬挂在微孔表面的OD基团吸收带的影响，以及H-2本身伸缩模式的诱导红外吸收带的行为。从观察到的光谱随时间和温度的变化可以看出，邻位-H-2到对-H-2的结构变化和弛豫都很明显。通过对H-2与无定形冰团表面相互作用的光谱的模拟，可以合理详细地解释复杂的光谱行为。该光谱以前是通过单个水分子的积累和松弛来研究团簇生长的经典轨迹研究中产生的。计算了相对于团簇表面H-2坐标的势能极小值，并通过将H-2、D2O相互作用划分为相对较弱的van der Waals相互作用以及H-2四极与H2O偶极和四极之间较强的静电相互作用，对吸附-表面成键提供了定性的解释。H-2与表面的净结合主要由与邻近D2O分子的几个van der Waals相互作用主导，但在大多数计算的极小值中，H-2也与表面分子形成单一的静电键。虽然这种静电键只提供了结合能的一小部分，但它们似乎对观察到的光谱有很大的影响。观察到的H-2诱导的悬垂OD带的移动似乎是由于H-2与悬垂外径的D原子的静电键合引起的，并且H-2强度的很大一部分被认为来自于H-2分子与表面悬垂的氧原子的静电键合。计算(不包含可调参数)很好地再现了测量光谱的几个特征，包括悬垂的OD带的分裂，该带由于H-2的结合而移动，以及H-2带的频率和宽度。
Infrared spectra are reported for thin films of deuterated microporous amorphous ice formed at 12 K and saturated with absorbed molecular hydrogen. This paper focuses on both the influence of the surface-bound H-2 on the absorption bands of the OD groups that dangle from the micropore surfaces and the behavior of the induced infrared bands of the stretching mode of H-2 itself. Both structural changes and the relaxation of ortho-H-2 to para-H-2 are apparent from variations in the observed spectra with time and temperature. A reasonably detailed interpretation of the complex spectral behavior has been possible through simulation of spectra for H-2 interacting with the surface of amorphous ice clusters generated previously in a classical trajectory study of the cluster growth through the accumulation and relaxation of individual water molecules. Potential minima were calculated with respect to H-2 coordinates on the cluster surface and a qualitative interpretation of adsorbate-surface bonding provided via the partitioning of the H-2..D2O interactions into relatively weak van der Waals interactions, and stronger electrostatic interactions between the H-2 quadrupole and the H2O dipole and quadrupole. The net binding of H-2 to the surface is dominated by several van der Waals interactions with neighboring D2O molecules, but in most of the calculated minima, H-2 also forms a single electrostatic bond to a surface molecule. While such electrostatic bonds provide only a small fraction of the binding energy, they appear to influence strongly the observed spectra. Observed H-2-induced shifts in the dangling OD bands appear to be caused by electrostatic bonding of H-2 to a D atom of a dangling OD and a significant fraction of the H-2 intensity is proposed to originate from H-2 molecules which are electrostatically bonded to dangling oxygen atoms on the surface. Calculations (which do not contain adjustable parameters) reproduce quite well several features of the measured spectra, including the splitting of the dangling OD band, the shift of this band due to binding of H-2, and the frequency and the width of the H-2 band.