Vibrational spectroscopy of fluidN2up to 34 GPa and 4400 K

Single-pulse multiplex coherent anti-Stokes Raman scattering (CARS) was used to observe the vibrational spectra of liquid ${\mathrm{N}}_2$ shock compressed to several pressures and temperatures up to 34 GPa and 4400 K. Vibrational frequencies, peak Raman susceptibilities, and Raman linewidths were determined for the fundamental and several excited-state transitions by comparing experimental spectra to synthetic spectra calculated using a semiclassical model for CARS intensities. The question of excited-state populations in the shock compressed state is addressed.