Time-resolved Raman spectra of nitromethane shocked to 140 kbar peak pressure using step wave loading have been obtained. The CN stretch (917 cm(-1)), CH3 stretch (2968 cm(-1)), and the NO2 stretch/CH3 bend (1400/1377 cm(-1)) vibrations are all observed to harden when peak pressure is attained in the liquid samples. The spectra obtained show no frequency softening up to 400 ns after peak pressure is reached in the material. Upon unloading from 140 kbar, the CN stretch vibration reverts back, showing no signs of an irreversible change. We also observe that the vibrational frequencies increase nonlinearly with peak pressure, with the CH3 stretching made exhibiting the largest increase. The observed frequency hardening and broadening are suggestive of strong intermolecular interactions at these shock pressures. Implications of these observations with regard to attaining a precursor state for shock-induced chemical reactions are discussed.