  We report the first coherent excitation of intramolecular vibrational modes
via the nonlinear interaction of a TeraHertz (THz) light field with molecular
liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences
with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then
measured in a terahertz Kerr effect spectrometer via phase-sensitive,
heterodyne detection with an optical pulse. The spectrometer reported here has
broader terahertz frequency coverage, and an increased sensitivity relative to
previously reported terahertz Kerr effect experiments. Vibrational coherences
are observed in liquid diiodomethane at 3.66 THz (122 cm$^{-1}$), and in carbon
tetrachloride at 6.50 THz (217 cm$^{-1}$), in exact agreement with literature
values of those intramolecular modes. This work opens the door to 2D
spectroscopies, nonlinear in terahertz field, that can study the dynamics of
condensed-phase molecular systems, as well as coherent control at terahertz
frequencies.
