Time resolution of chirped lattice vibrations in a mixed-valence metal-halogen complex system

Abstract

A quasi-one-dimensional metal-halogen complex, [Pt(en)(2)][Pt(en)(2)Br-2](ClO4)(4), has been investigated by a pump-probe measurement using sub-5-fs ultrashort white light pulses. The signal as a difference absorption was highly resolved both in time and frequency domains. By means of linear prediction-singular value decomposition calculation, four vibration modes, pairs of well-known and unknown modes, were retrieved, while almost no overtone was retrieved. Our analysis based on the dynamical matrix well explained the origin of one of the unknown modes. In addition, we found one more chirped low-frequency modulation in the slow-varying component of the signal, which is the first observation of a cluster motion of many lattice points and energy dissipation along the one-dimensional chain in this system.