Anomalous temperature dependence of the vibrational lifetime of the OD stretch vibration in ice and liquid water

The temperature dependence of the vibrational T 1 lifetime of the OD stretch vibration of HDO in H₂O ice was measured with femtosecond mid-IR pump-probe spectroscopy. We found an increase of T 1 from 480 ± 40 fs at 25 K to 860 ± 60 fs at 265 K. These lifetimes are remarkably shorter than the vibrational lifetime of the OD stretch vibration of HDO in H₂O in the liquid phase, which has a value of 1.7 ± 0.1 ps at 274 K and increases to 2.24 ± 0.09 at 343 K. The observed temperature dependence of T 1 can be well explained from a relaxation mechanism in which the OD vibration relaxes via energy transfer to the bend–libration combination tones of H₂O and HDO