Transient hole-burning spectroscopy of associated ethanol molecules in the infrared: Structural dynamics and evidence for energy migration

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Abstract
Hydrogen-bonded ethanol molecules in internal positions of oligomers are investigated in solutions of carbon tetrachloride (concentration 0.17 M). After resonant excitation of the OH-stretching vibration by a 2-ps infrared pump pulse at 3340 cm−1, transient spectral hole burning within the inhomogeneously broadened band is observed with a delayed, independently tunable probing pulse of 1 ps duration. Evidence is presented that the vibrational excitation migrates along the oligomer chain with subsequent breaking of H bonds so that additional ethanol dimers and trimers are formed. Correspondingly, the number of ethanol monomers or hydroxilic groups with proton acceptor function is found to increase. Several time constants describing the various processes, e.g., the proposed migration of vibrational quanta along the H bonded chain, breaking of hydrogen bonds, and the reassociation of the generated shorter species, are determined by a comparison of the experimental data with model computations.