1,1’-二羟基-5,5’-联四唑二羟胺盐(TKX-50)为新合成的高能炸药。 利用密度泛函理论计算研究TKX-50及其氘代物的太赫兹光谱, 探讨压强和氘代对THz光谱的影响。 结果表明, TKX-50有四个低频峰, 分别是1.17, 1.19, 2.50和2.95 THz; 有六个高频峰, 分别位于3.87, 4.79, 5.33, 5.75, 6.65和7.85 THz。 上述特征峰中, 1.17, 3.87, 5.33和6.65 THz吸收强度较大。 正则振动模式分析表明1.17 THz吸收峰归属于N—H…O伸缩振动, 3.87, 5.33和6.65 THz峰则主要属于NH₃摇摆振动。 在0~4.0 THz波段内, 与TKX-50的1.17, 1.91, 2.50, 2.95和3.87 THz吸收峰相对应的氘代物吸收峰分别是1.13, 1.85, 2.44, 2.91和3.63 THz。 氘代导致TKX-50的THz峰发生红移, 并且吸收峰强度降低。 氘代导致NH₃摇摆振动所产生的4.79和5.33 THz两个峰发生重叠和红移, 变为4.66 THz。 随着压强的变化, 分子间距离的变化大于键长的变化。 分子间O…H距离通常随压力的增加而减小, 特别是NO…HN距离。 然而, O—H和N—H键长度随压力的变化呈现不规则地变化。 在1 atm~30 GPa压力下, 其4.79, 5.33和5.75 THz峰因压力的诱导作用, 谱带发生红移和重叠, 并伴随吸收强度产生较大变化; 在30 GPa时, 重叠为4.54 THz一个弱吸收峰。 随压强的增加, 6.65 THz的吸收峰略微蓝移, 而7.85 THz的吸收峰先红移后逐渐蓝移。 这是因为当压力增加时, 原子间平衡距离减小, 将导致化学键增强; 另外, 当晶体被严重压缩时, NH₃的摇摆振动空间位阻变大, 需要克服较大的势能, 导致吸收峰向短波方向移动。 低频峰则随压强的变化呈现不规则变化, 主要是因为N—H键长度随压力的变化表现为不规则地变化。 由于高压下的分子振动受到空间位阻限制, 振幅减小, 其THz谱吸收强度随着压力的增加而降低。 上述研究不仅揭示TKX-50的THz光谱特征及其压力和同位素效应, 而且为进一步研究同类含能材料分子在THz波段的光学性质及其快速穿透性检测提供理论依据。

Dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate (TKX-50) is a newly synthesized high energetic explosives. Density functional theory calculations were carried out to study the terahertz (THz) spectra of TKX-50 and its pressure and isotope effects. The results show that TKX-50 has four peaks in low frequencies of 1.17, 1.19, 2.50 and 2.95 THz, and six absorption peaks at high frequencies of 3.87, 4.79, 5.33, 5.75, 6.65 and 7.85 THz. Among them, four peaks at 1.17, 3.87, 5.33 and 6.65 THz have large absorption intensities. Vibrational analyses of normal modes show that the absorption peak at 1.17 THz belongs to the N—H…O stretching; and those at 3.87, 5.33 and 6.65 THz are attributed to the NH₃ rocking. In the 0~4.0 THz, the absorption peaks of 1.17, 1.91, 2.50, 2.95 and 3.87 THz for TKX-50 correspond to the peaks of 1.13, 1.85, 2.44, 2.91 and 3.63 THz for the deuterated TKX-50, respectively. The deuteration of TKX-50 brings about the red shifts of THz spectra along with the absorption intensities decreasing at the same time. In addition, the peaks at 4.79 THz and 5.33 THz for TKX-50, which are assigned to the rocking of NH₃, become overlapped and redshifted to 4.66 THz due to deuteration. As the pressure changes, the variations of molecular distances are larger than those of bond lengths. The intermolecular O…H distance generally decreases with increasing pressure, especially the NO…HN distance. However, the lengths of the O—H and N—H bonds irregularly vary with pressures. When the pressure increases from 1 atm to 30 GPa, the peaks at 4.79, 5.33 and 5.75 THz will red shift and overlap, accompanied by a larger change of absorption intensity. Then at 30 GPa, the absorption peaks overlap to a weak peak at 4.54 THz. With increasing pressure, the absorption at 6.65 THz is slightly blue shifted, while the peak at 7.85 THz is red shifted firstly but then gradually blue shifted. This is because the atomic equilibrium distance decreases with increasing pressure, leading to an increase in bond strength; in addition, when the crystal is severely compressed, the steric hindrance for the NH₃ rocking becomes large, and large potential energy needs to overcome for the rocking, resulting in a blue shift of THz absorption. The low frequency peaks irregularly vary with pressures, mainly because the length of the N—H bond varies irregularly with pressures. Since the vibrational movements of the molecule are constrained by the steric hindrance at high pressures, the THz absorption intensities of TKX-50 decrease with increasing pressure. The above studies not only reveal the THz spectral characteristics of TKX-50 and the effects of pressure and isotope but also provide the theoretical basis for further study of the optical properties in THz region and their application in rapid penetrable detections for similar energetic materials.