Vibrational dynamics of the C-O stretch vibrational in alcohols

We present a study on the vibrational dynamics of the C–O stretch vibration of methanol and ethanol in carbon tetrachloride (CCl₄) solution. The relaxation of the excited C–O stretch vibration was observed to occur in two steps. In the first step energy is transferred from the v = 1 state of the C–O stretch vibration to an intermediate state with a time constant of 3.2±0.2 ps for methanol and 3.2±0.7 ps for ethanol. The intermediate state is most likely formed by the n = 3 or 4 state of the C–O–H bending mode, which is also known as the torsional mode. In the second step energy is transferred from this intermediate state to low-energy modes, leading to a full equilibration of the energy. In methanol this thermalization occurs with a time constant of 28±1ps. In ethanol the second step is faster, with a time constant of 12±2 ps.