Non-Markovian Dynamics of the Vibrations of Ions in Water from Femtosecond Infrared Three-Pulse Photon Echoes

The first femtosecond three-pulse photon echo experiment of a vibrational transition is presented. A mode of the azide ion N₃^- at 2043cm^-1 is used to probe the impulsively excited vibrational energy distribution and hence the dynamics of the water around the ion. The vibrational frequency correlations decay on time scales of about 80 fs and 1. 3 ps, while a small part remains for longer than about 10 ps. The 1. 3 ps decay is the residence time for hydrogen bonds to the ion. Major differences between vibrational and optical three-pulse echoes are addressed.