Direct measurement of vibrational energy relaxation in photoexcited deoxyhemoglobin using picosecond Raman spectroscopy

We have directly observed hot vibrations in photoexcited deoxyhemoglobin. The data quantitatively indicate a heme vibrational temperature of 20 K above room temperature within the time sampled by an 8ps laser pulse. The slow component of vibrational relaxation occurs with a rate constant of (2-5ps)-1. Similar dynamics are observed in oxhemoglobin. The initial stages of recombination of O2 with the heme following photodissociation of oxyhemoglobin are observed in the transient vibrational spectrum. Contrary to previous work, we do not observe the influence of protein dynamics on O2 recombination