Ultrafast shock-induced chemistry in carbon disulfide probed with dynamic ellipsometry and transient absorption spectroscopy

Abstract

We used transient visible/near-infrared absorption spectroscopy and ultrafast dynamic ellipsometry to characterize carbon disulfide (CS2) shocked with an ultrafast laser pulse. We found a volume-decreasing reaction, characterized by the deviation of the shock and particle velocity (us and up) points from the unreacted Hugoniot, above up = 1.5 km/s. This result contrasts with literature plate-impact data, which found the reaction-induced deviation from the unreacted Hugoniot to occur at up = 1.2 km/s. We attribute this disparity to the difference in timescale between plate-impact experiments (ns to μs) and our ultrafast experiments (sub-ns), as our ultrafast experiments require higher shock pressures and temperatures for an observable reaction. The volume-decreasing reaction was accompanied by a large increase in absorption of the reaction products, necessitating the use of impedance matching techniques to characterize the us-up points above the reaction cusp. Using transient absorption spectroscopy, we discovered a change in the absorption spectrum for shock strengths below and above the volume-decreasing reaction, suggesting there are multiple chemical reactions in CS2 shocked to above 7.4 GPa in 300 ps.