Pump–probe polarized transient hole burning (PTHB) dynamics of hydrated electron revisited

Femtosecond PTHB spectroscopy was expected to demonstrate the existence of distinct s–p absorption subbands originating from the three nondegenerate p-like excited states of hydrated electron in anisotropic solvation cavity. Yet no conclusive experimental evidence either for this subband structure or the reorientation of the cavity on the picosecond time scale has been obtained. It is shown here that rapid reorientation of s–p transition dipole moments in response to small scale motion of water molecules is the likely culprit. The polarized bleach is shown to be too low in amplitude and too short lived to be observed reliably on the sub-picosecond time scale.