We present direct evidence for coherent vibrational motions of low frequency in the v = 0 ground state of the high-frequency O-D stretching mode of an intramolecular hydrogen bond. Femtosecond mid-infrared pump-probe studies of hydroxy-deuterated 2-(2'-hydroxyphenyl)benzothiazole in toluene reveal an oscillatory change of O-D stretching mode absorption persisting for several picoseconds after excitation. An infrared resonantly enhanced stimulated Raman process within the bandwidth of the pump pulse creates a vibrational wave packet which is made up of quanta of a 118 cm(-1) mode modulating the length of the hydrogen bond and thus the O-D stretching absorption band.