Picosecond Dynamics of 'Davydov Soliton' Absorption Band in Acetanilide Using Infrared Free Electron Laser

It has been suggested that the 1650 cm sup -1 band in the ir spectrum of Acetanilide at low temperatures is the absorption band of a nonlinear excitation of soliton variety, similar to that proposed by Davydov in alpha-helix proteins. We report the results of picosecond transient bleaching experiments on polycrystalline Acetanilide using the high intensity ~2 ps pulses from the Mark III ir Free Electron Laser. We find large bleaching signals with a rise time less than the duration of the laser pulse.