Transient infrared absorption of diluted HDO/D2O solutions is measured with
150 fs laser pulses. The signal intensity decays in a heavily non-exponent
ial way, and its variation is often non-monotonic; no quantum beats are obs
erved. These effects are ascribed to the simultaneous presence of solvent a
nd population dynamics in low lying vibrational states, and to a partial ca
ncellation of the bleach and absorption intensities. (C) 2001 Elsevier Scie
nce B.V. All rights reserved.