Hydrogen Bond Networks: Structure and Evolution after Hydrogen Bond Breaking

The nature of hydrogen bonding networks following hydrogen bond breaking is investigated using vibrational echo correlation spectroscopy of the hydroxyl stretch of methanol-OD (MeOD) of MeOD oligomers in CCl4. Using ultrafast (<50 fs) infrared multidimensional stimulated vibrational echo correlation spectroscopy with full phase information, the experiments examine frequency correlation between initially excited OD stretches and their “photoproducts ” created by hydrogen bond breaking following vibrational relaxation. The hydrogen bond breaking following vibrational relaxation gives rise to a new species, singly hydrogen bonded MeODs, the photoproduct. The photoproducts give rise to a well-defined spectrally distinct off-diagonal peak in the correlation spectrum. Detailed modeling of this peak is used to measure its spectral diffusion (increased spectral broadening as time increases). A rephasing vibrational echo signal and spectral diffusion can only occur if photoproduct hydroxyl stretch frequencies are highly correlated with the frequencies of the initially excited hydroxyl stretches prior to hydrogen bond breaking. The observation of spectral diffusion (fine frequency correlation) demonstrates that broken oligomers have “memory ” of initial unbroken oligomers. Possible explanations for the frequency correlation are discussed. I