Dynamics of vibrational and electronic coherences in the electronic excited state studied in a negative-time range

Femtosecond pump–probe spectroscopy signals in a negative-time range (i.e., when the probe pulse precedes pump pulse) were analyzed to study the dynamics of electronic and vibrational coherences in the photodissociation of oxyhemoglobin. The decay time of the electronic coherence between the ground and Q-band electronic states is found to be 45 ± 5 fs. The dephasing times of the vibrational modes of several frequencies in the ground state have been determined. Those in the excited state are found to be ∼26 fs. The absence or presence of the modes in the negative-time range due to the excited state wavepacket is explained in terms of the mode coupling strength.