In situRaman spectroscopy of shock-compressed benzene and its derivatives

Abstract

Real-time Raman spectra of shock compressed benzene and its monosubstitutes, iodobenzene, and nitrobenzene, have been measured in the pressure range up to 7.5 GPa. Spectral peaks show almost linear blueshifts against shock pressure. However, nitrobenzene, compared to the other two compounds, shows smaller shifts. Especially the increase in Raman frequency of the NO 2 stretching mode ͑1346 cm Ϫ1 ͒ is extremely small. An intermolecular interaction between nitrobenzene molecules seems responsible for this behavior.In order to understand shock-induced phenomena, it is essential to obtain real-time information of materials under shock compression. The dynamic nature of shock compression, i.e., fast rise, short duration, and fast release of shock loading, often generates nonequilibrium states or unstable intermediates in the process of shock compression and usually they are not quenchable. In situ laser spectroscopy is a good tool to investigate those transient states or species. It can provide real-time information on shock-induced structural and chemical changes. Some sophisticated applications of laser spectroscopy to in situ observation of shock-induced phenomena have been reported over the last couple of decades. 1-6 In this paper we report shock-induced changes in vibrational spectra of benzene, iodobenzene, and nitrobenzene measured by a single-pulse laser Raman spectrometer in conjunction with a plate impact technique. It was found that shock-induced changes in Raman spectra of nitrobenzene are quite different from those of benzene and iodobenzene. Spectral peak shifts ͑blue shifts͒ against shock pressure were found smaller for nitrobenzene compared to those of benzene and iodobenze, especially the NO 2 stretching mode of nitrobenzene showed very small shifts. The relatively strong intermolecular interaction existing between nitrobenzene molecules seems to play an essential role. In this study we determined Raman frequency changes against shock pressures for three very common organic solvents. This kind of data can also be used as pressure calibration standards for certain shock experiments. For example, unlike shock experiments by plate impact, in some laser shock experiments pressure determination is difficult and may involve large uncertainties. In such cases, shock pressures can be easily determined by measuring the spectral shift for a standard sample whose spectral peak shift vs shock pressure data are available.In general vibrational frequencies of stretching modes increase with pressure because bond lengths are reduced 7 under pressure and effective force constants at the new equilibrium positions are usually larger than those at the original equilibrium position. This simplified description is qualitatively valid at relatively low pressures where the compression energy is small compared to the electronic energies. 8

Time‐resolved Raman spectroscopy of polystyrene under laser driven shock compression

“…Hence, by coupling of the laser‐driven shock with ultrafast optical excitation and with suitable probes, it is possible to observe molecular vibrations in real time under shock compression with picosecond time resolution . So, to investigate molecular and chemical changes in the real time frame under shock compression and shock loading, time‐resolved Raman spectroscopy becomes quite useful . Many interesting applications of Raman spectroscopy in observing shock induced phenomena on polymers have been reported over the last couple of decades .…”

“…[5,22,23] So, to investigate molecular and chemical changes in the real time frame under shock compression and shock loading, time-resolved Raman spectroscopy becomes quite useful. [24][25][26][27][28] Many interesting applications of Raman spectroscopy in observing shock induced phenomena on polymers have been reported over the last couple of decades. [1,[29][30][31][32][33][34] For example, Hare and Dlott [33] studied the dynamics of poly-methyl methacrylate (PMMA) micro gauge undergoing photo-thermal laser ablation by picosecond coherent Raman spectroscopy and indicated the generation of monomer due to thermal decomposition.…”

In Situ Raman Spectroscopic Studies of Liquid Carbon Tetrachloride (CCl4) Under Static and Laser-Driven Shock Compression

“…Time-resolved Raman spectroscopy (TRRS) is one such tool used to investigate these transient states or species which provide real-time information on shock-induced structural and chemical changes occurring when the sample is traversed by shock. 9 Because of the temporal nature of shock wave loading, time-resolved measurements can permit real-time examination of structural, symmetry, and chemical changes occurring due to shock-induced phenomena. Time-resolved Raman spectroscopy acts as an instantaneous probe for measurement of temperature, pressure, and reactivity of a shocked material.…”

Time‐resolved Raman studies on Al2O3: Cr3+: lifetime measurements of the excited‐state transition Ē → 2Ā

“…In the last 10 years, the availability of intensified charge coupled device (ICCD) cameras has opened up new possibilities in Raman spectroscopy, especially for time‐resolved measurements. Thus, recently, a few time‐resolved Raman experiments through ICCD detection have been reported in different approaches, for example, in the depth analysis of diffusely scattering media,8 in the study of matter under shock compression9–15 and in the study of transient species in solution,16–18 but the use of ICCD detection has not yet been extended to study the dynamic phenomena happening in the solid state with a two‐color system or pump–probe‐based methods.…”