The first picosecond infrared vibrational echo experiments on a protei
n, myoglobin-CO, are described. The experiments were performed at temp
eratures ranging from 60 to 300 K with a midinfrared free electron las
er tuned to 1945 cm(-1). Below similar to 185 K, the pure dephasing, T
-2, displays a power law temperature dependence, T-1.3. This behavior
is reminiscent of that associated with the properties of low temperat
ure glasses (<5 K) but is observed here at much higher temperatures. A
bove the solvent glass transition temperature, T-2 is exponentially a
ctivated.