Ultrafast vibrational dynamics of doubly hydrogen bonded acetic acid dimers in liquid solution

Acetic acid dimers in liquid CCl4 have been studied by picosecond infrared double resonance spectroscopy in the 2000 to 3800 cm−1 region. A subpicosecond redistribution of the vibrational energy among the various modes within the broad OH band of the hydrogen-bonded dimer ring was found; an effective vibrational lifetime of 4.0±1.5 ps was measured for the whole ensemble. The additionally observed slower decay component of 15 ps is attributed to nanoscopic thermal diffusion and the reaction of the hydrogen bond system to the elevated temperature.