Bowlan Pamela, Powell Michael, Perriot Romain, Martinez Enrique, Kober Edward M, Cawkwell M J, McGrane Shawn
Physical Chemistry and Applied Spectroscopy, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Shock and Detonation Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Chem Phys. 2019 May 28;150(20):204503. doi: 10.1063/1.5092242.
We probe shock-induced chemistry in two organic liquids by measuring broadband, midinfrared absorption in the 800-1400 cm frequency range. To test this new method and understand the signatures of chemical reactions in time resolved vibrational spectra, we compared liquid benzene shocked to unreactive conditions (shocked to a pressure of 18 GPa for a duration of 300 ps) to nitromethane under reactive conditions (25 GPa). We see clear signatures of shock-induced chemistry that are distinguishable from the pressure- and temperature-induced changes in vibrational mode shapes. While shocked benzene shows primarily a broadening and shifting of the vibrational modes, the nitromethane vibrational modes vanish once the shock wave enters the liquid and simultaneously, a spectrally broad feature appears that we interpret as the infrared spectrum of the complex mixture of product and intermediate species. To further interpret these measurements, we compare them to reactive quantum molecular dynamics simulations, which gives qualitatively consistent results. This work demonstrates a promising method for time resolving shock-induced chemistry, illustrating that chemical reactions produce distinct changes in the vibrational spectra.
我们通过测量800 - 1400厘米频率范围内的宽带中红外吸收，来探究两种有机液体中由冲击引发的化学反应。为了测试这种新方法并了解时间分辨振动光谱中化学反应的特征，我们将冲击到非反应条件下（冲击到18吉帕压力，持续300皮秒）的液态苯与处于反应条件下（25吉帕）的硝基甲烷进行了比较。我们看到了冲击引发化学反应的清晰特征，这些特征与振动模式形状中由压力和温度引起的变化是可区分的。虽然冲击后的苯主要表现为振动模式的展宽和位移，但一旦冲击波进入液体，硝基甲烷的振动模式就会消失，同时会出现一个光谱展宽的特征，我们将其解释为产物和中间物种复杂混合物的红外光谱。为了进一步解释这些测量结果，我们将它们与反应性量子分子动力学模拟进行了比较，模拟结果在定性上是一致的。这项工作展示了一种用于时间分辨冲击引发化学反应的有前景的方法，表明化学反应会在振动光谱中产生明显的变化。
