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

The temperature dependence of the vibrational T1 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 T1 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 T1 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.