Raman spectroscopic studies of ortho-xylene under laser driven shock and static compression

Abstract

Ortho-xylene (o-xylene), a derivative of benzene and an important aromatic compound is applied as an anti-knocking agent in automobiles and jet engines. Knocking being a dynamical phenomenon that occurs at very high temperatures and high pressures, here we have reported the pump–probe technique based time-resolved Raman spectroscopy studies under laser-driven shock compression (high temperature and high pressure) along with the numerical simulation to understand the molecular level response of o-xylene under shock compression. The laser shock experiments carried out up to 4.1 GPa using confinement geometry target holder assembly show indication of three phase transitions, i.e., liquid–solid phase-I, solid phase-I–solid phase-II, and solid phase-II–solid phase-III at 1.2, 2.1, and 3.6 GPa, respectively. The shock velocities calculated for 700 mJ laser energy (corresponding pressure 2.5 GPa) using intensity ratios of Raman modes scattered from the shocked and whole region of the sample for 735 and 582 cm−1 Raman modes are 3.4 ± 0.3 and 3.5 ± 0.3 km/s, respectively, which is in close agreement with the shock velocity of 3.51 km/s determined using 1D radiation hydrodynamic numerical simulation. In addition, our high-pressure static compression studies on this compound employing diamond anvil cell up to 13 GPa show that this compound shows four possible phase transitions at 0.4, 0.9, 3.8, and 12 GPa pressures to solid phase I, II, III, and IV, respectively. On release, these phase transitions are reversible.