高压下1,1’-二羟基-5,5’-联四唑二羟胺盐的振动光谱及同位素效应

用密度泛函理论方法研究1,1’-二羟基-5,5’-联四唑二羟胺盐(HATO)晶体在高压(<40 GPa)下性质。在GGA-PW91计算水平并结合超软势基组对HATO晶体结构进优化，其优化结构能再现实验结果。分子间O…H间距随压力的增加而显著减小；但O—H和N—H键长呈现非单调变化。基于不同压力下的优化晶体结构，利用非周期性计算并经校正因子0.967 9校正，求得相应压力下的红外和拉曼谱。预测最强拉曼峰对应于C—C伸缩和NH₂对称变形，位于1 580 cm-1，与实验结果一致。虽然阴离子不含氢原子，但阳离子的氘代仍对阴离子的振动光谱产生影响。高压导致分子间氢键增强，导致参与氢键的O—H和O—D振动的拉曼波数减小。氘代后，ND₂的拉曼位移的最明显变化是ν₂伸缩振动波数在高压下急剧增加，导致ND₂ ν₂/ν₃在高压下发生偶合。计算出的ν₁至ν₃振动的同位素效应比ν(NH₂)/ν(ND₂)均为1.36～1.38，与由折合质量所求得的值相一致。氘代和压力的变化可引起不同振动模式的偶合。

Vibrational Spectra and Isotope Effect of Dihydroxylammonium 5,5’-Bis(Tetrazole)-1,1’-Diolate under High Pressure

Density functional theory calculations were performed on crystalline dihydroxylammonium 5,5’-bis(tetrazole)-1,1’-diolate (HATO) under high pressure up to 40 GPa. The GGA-PW91 method in combination with the ultrasoft pseudopotentials reproduced the experimental crystal structure of HATO and was thus employed for the optimizations of both molecular structure and cell parameters. The intermolecular O…H distances generally decrease with increasing pressures. However, the O—H and N—H bond lengths change irregularly upon pressure. Based on the optimized crystal structures at different pressures, the non-periodic calculations of frequencies with a scaling factor of 0.967 9 were used to predict both the IR and Raman spectra. The predicted strongest Raman peak at 1 580 cm-1, involving C—C stretching and NH₂ symmetric deformation, is in agreement with the experiment. Although there is no hydrogen atom in the anion moiety of HATO, the deuteration in cation still affects the vibrational mode of anion. For O—H and O—D vibration modes, the Raman shifts decrease due to the strengthening intermolecular hydrogen bond as the pressure increases. Upon deuteration, the most characterized change of Raman shifts for ND₂ is that the ν₂ stretching mode increases dramatically with high pressure as compared to those of NH₂, which leads to a coupling of ND₂ ν₂/ν₃ modes at high pressure. The calculated isotopic ratios, ν(NH₂)/ν(ND₂) for ν₁ to ν₃ modes, are in the range of 1.36～1.38, which are in consistent with the value from the reduced masses of these atoms. The couplings of vibrational modes change with both deuteration and pressure.