Vibrational relaxation of D2O in As2S3

The vibrational relaxation of polyatomic molecular impurities in solids is controlled by a decay scheme that involves both internal modes and vibrational quanta of the host material. Here the relaxation of the asymmetric stretch mode of D2O in vitreous As2S3 is reported. Applying a pump-probe technique using infrared laser pulses of the Stanford Picosecsnd Free Electron Laser, a relaxation time on the order of 200 ps at low temperature is found. From the temperature dependence of the relaxation time, it is concluded that the asymmetric stretch mode relaxes in a process involving two bending modes of the D2O molecule and two vibrational quanta of the host.