Vibrational coherence in Azurin with impulsive excitation of the LMCT absorption band

We report the results of femtosecond pump–probe measurements on Azurin, a blue copper protein. The decay of the pump-induced ground-state bleaching, following the excitation of the ligand-to-metal charge-transfer absorption band, is modulated by well visible oscillations and occurs exponentially with a time constant of about 270 fs. The Fourier transform of the oscillatory component, besides providing all the vibrational modes found by conventional resonance Raman, presents additional bands whose attribution is discussed also in connection with the protein dynamics.