Power Dependent Behavior of Myoglobin Raman Modes in the Picosecond Time Region.

The power dependent behavior of the transient Raman spectra of deoxy and carboxy myoglobin have been studied using ~30 ps laser pulses. The width and frequency of the Raman mode sensitive to porphyrin pi-electron density, nu sub 4 varies approximately linearly with incident photon density. Also, the coresize density marker, nu sub 2, shifts to lower frequency at high photon densities. The implications of these results for recent picosecond transient Raman studies are discussed. The power dependent behavior of these modes is considered in terms of recent work by several groups. Possible origins of this phenomenon include heating of the heme by photon absorption, build up of an excited electronic state population of hemes or a non-linear excitation process.