Energy transfer in single hydrogen-bonded water molecules

We study the structure and dynamics of hydrogen-bonded complexes of H₂O/HDO and acetone dissolved in carbon tetrachloride by probing the response of the O-H stretching vibrations with linear mid-infrared spectroscopy and femtosecond mid-infrared pump-probe spectroscopy. We find that the hydrogen bonds in these complexes break and reform with a characteristic time scale of approximate to 1 ps. These hydrogen-bond dynamics are observed to play an important role in the equilibration of vibrational energy over the two O-H groups of the H₂O molecule. For both H₂O and HDO, the O-H stretching vibrational excitation relaxes with a time constant of 6.3 ± 0.3 ps, and the molecular reorientation has a time constant of 6 ± 1 ps.