Vibrational Förster transfer in ice Ih.

We have studied Förster energy transfer between O-H vibrations in H(2)O/D(2)O ice Ih using femtosecond, two-color, mid-infrared pump-probe spectroscopy. We found that as a result of couplings to nearby O-H stretch modes, the vibrational relaxation time decreases from 480 fs for dilute HDO in D(2)O down to 300 fs for pure H(2)O ice. The anisotropy shows an initial 140 fs decay down to a concentration-dependent end level. This end level for low concentrations can be explained from the limited rotational freedom ( approximately 20 degrees ) of a water molecule in the ice lattice over time scales > 15 ps. The decreasing end levels for higher concentrations of H(2)O result from Forster energy transfer to the next-nearest six O-H groups. No Förster transfer beyond these neighbors is observed. Variation of the ice temperature between 200 and 270 K was found to have negligible effect on the dynamics.