Coherent Raman Studies of Shocked Liquids

Coherent anti-Stokes Raman spectroscopy (CARS) is reported following shock loading for the liquids phenylacetylene (18 and 13 GPa), cyclohexane (17 GPa), and acrylonitrile (17 GPa). The evolution of the spectra over the first 300 ps was recorded in each case. All spectra show monotonic decay of all peaks with increasing time after shock. No new peaks due to either chemical reaction or pressure shifting of the vibrational frequencies were observable. This loss of signal after shock is attributed to the decreased coherence time in the shock heated liquids, which leads to rapid signal loss in the nonresonant background free version of CARS used in the measurements. These results suggest that more complex methods may be required to measure picosecond shock induced chemistry with coherent Raman techniques that are free of nonresonant background interference.