IR Spectroscopy of Hydrogen-Bonded Methanol:  Vibrational and Structural Relaxation on the Femtosecond Time Scale

Two-color pump−probe spectroscopy is performed with femtosecond time resolution in the OH-stretching region of methanol oligomers in a CCl 4 mixture at room temperature. The measured isotropic component of the probe transmission signal gives direct access to the lifetime of the OH-stretching vibration. It varies between 0.45 and 0.6 ps, increasing with excitation frequency from 3280 to 3400 cm -1 . After vibrational excitation of the OH-mode, fast spectral relaxation and/or vibrational energy migration with subsequent breaking of the excited oligomers is noticed. Recombination proceeds with a time constant of 9 ps. Comparison to earlier work on water and related alcohols is also made.