Coherent vibrational ground-state dynamics of an intramolecular hydrogen bond

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.