S. Woutersen et al., A FEMTOSECOND MIDINFRARED PUMP-PROBE STUDY OF HYDROGEN-BONDING IN ETHANOL, The Journal of chemical physics, 107(5), 1997, pp. 1483-1490
We present a femtosecond midinfrared pump-probe study of hydrogen bond
ing. It is shown that upon excitation of the OH-stretching vibration o
f hydrogen-bonded ethanol dissolved in CCl4, the hydrogen bonds are pr
edissociated on a femtosecond time scale. The measured predissociation
time constant depends strongly on the excitation frequency, and range
d from similar to 250 fs at 333 cm(-1) to similar to 900 fs at 3450 cm
(-1). The time constant of the subsequent reassociation of the hydroge
n bonds was found to be 15 ps, in accordance with previous picosecond
studies. Furthermore, polarization-resolved measurements show that ori
entational relaxation takes place on a time scale much shorter than th
e pulse length of similar to 200 fs. This rapid orientational relaxati
on can be explained from the fast delocalization of the O-H stretching
excitation over the hydrogen-bonded ethanol oligomers. The orientatio
nal anisotropy R reaches a value of 0.15 instantaneously, and remains
constant for all delays. (C) 1997 American Institute of Physics.