Femtosecond vibrational dynamics of self-trapping in a quasi-one-dimensional system

We have directly time resolved the lattice motions associated with the formation of the self-trapped exciton in the quasi-one-dimensional system Pt(en)(2)] Pt(en)2Br2];(PF6)(4) ( en = ethylene-diamine, C2H8N2), using femtosecond impulsive excitation techniques. A strongly damped, low-frequency wave packet modulation at approximately 110 cm(-1) accompanies the formation of the self-trapped exciton on a approximately 200 fs time scale following excitation of the intervalence charge-transfer transition. Coherent oscillations at the ground state vibrational frequency and its harmonics are also detected.