Powell M S, Sakano M N, Cawkwell M J, Bowlan P R, Brown K E, Bolme C A, Moore D S, Son S F, Strachan A, McGrane S D
Maurice J. Zucrow Laboratory, Mechanical Engineering Department, Purdue University, 500 Allison Rd., West Lafayette, Indiana 47907, United States.
Shock and Detonation Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
J Phys Chem A. 2020 Sep 3;124(35):7031-7046. doi: 10.1021/acs.jpca.0c03917. Epub 2020 Aug 19.
Thin films of pentaerythritol tetranitrate (PETN) were shock compressed using the laser driven shock apparatus at Los Alamos National Laboratory (LANL). Two spectroscopic probes were available to this apparatus: visible white light transient absorption spectroscopy (VIS) from 400 to 700 nm and mid-infrared transient absorption spectroscopy (MIR) from 1150 to 3800 cm. Important PETN vibrational modes are the symmetric and antisymmetric NO stretches at 1280 and 1650 cm, respectively, as well as CH stretches at ∼2900 cm. Shock strength was varied from approximately 3 to 55 GPa to span from the chemically unreactive regime to the regime in which fast chemical reaction took place on the 250 ps time scale of the measurements. VIS and MIR results suggest irreversible chemistry was induced in PETN at pressures above 30 GPa. At lower shock pressures, the spectroscopy showed minimal changes attributable to pressure induced effects. Under the higher-pressure reactive conditions, the frequency region at the antisymmetric NO stretch mode had a significantly increased absorption while the region around the symmetric NO stretch did not. No observable increased absorption occurred in the higher frequency regions where CH-, NH-, and OH- bond absorptions would be observed. A broad absorption appeared on the shoulder at the red-edge of the CO vibrational band around 2200 cm. In addition to the experiments, reactive molecular dynamics were carried out under equivalent shock conditions to correlate the evolution of the infrared spectrum to molecular processes. The simulations show results consistent to experiments up to 30 GPa but suggest that NO and NO related features provided the strongest contributions to the shocked infrared changes. Proposed mechanisms for shocked PETN chemistry are analyzed as consistent or inconsistent with the data presented here. Our experimental data suggests C≡O or NO bond formation, nitrite formation, and absence of significant hydroxyl or amine concentrations in the initial chemistry steps in PETN shocked above 30 GPa.
利用位于洛斯阿拉莫斯国家实验室（LANL）的激光驱动冲击装置对季戊四醇四硝酸酯（PETN）薄膜进行了冲击压缩。该装置配备了两种光谱探测手段：400至700纳米的可见白光瞬态吸收光谱（VIS）以及1150至3800厘米⁻¹的中红外瞬态吸收光谱（MIR）。PETN的重要振动模式分别为1280厘米⁻¹和1650厘米⁻¹处的对称和反对称NO伸缩振动，以及约2900厘米⁻¹处的CH伸缩振动。冲击强度在大约3至55吉帕之间变化，涵盖从化学惰性状态到在测量的250皮秒时间尺度上发生快速化学反应的状态。VIS和MIR结果表明，在压力高于30吉帕时，PETN中引发了不可逆化学反应。在较低的冲击压力下，光谱显示出归因于压力诱导效应的微小变化。在较高压力的反应条件下，反对称NO伸缩模式的频率区域吸收显著增加，而对称NO伸缩附近区域则没有。在可观察到CH -、NH -和OH -键吸收的较高频率区域未出现可观察到的吸收增加。在约2200厘米⁻¹处的CO振动带红边肩部出现了一个宽吸收峰。除了实验之外，还在等效冲击条件下进行了反应性分子动力学模拟，以将红外光谱的演变与分子过程相关联。模拟结果显示，在高达30吉帕时与实验结果一致，但表明NO和与NO相关的特征对冲击后的红外变化贡献最大。分析了所提出的冲击PETN化学反应机制与本文所呈现数据的一致性或不一致性。我们的实验数据表明，在压力高于30吉帕冲击PETN的初始化学步骤中，会形成C≡O或NO键、亚硝酸盐，且不存在显著浓度的羟基或胺。
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