Time - resolved studies of NO 2 photoinitiated unimolecular decomposition : step - like variation of kuni

Time-resolved, subpicosecond-resolution measurements of NO2 photoinitiated unimolecular decay rates are reported for jetcooled samples in the vicinity of the dissociation threshold. The molecules are excited by 385-400 nm tunable subpicosecond pulses to the *Bz electronic state which is very strongly mixed with the 2A, ground electronic state. Subsequent decomposition is probed by a 226 nm subpicosecond pulse which excites LIF in the NO product. When changing the amount of energy in excess of the dissociation threshold, a step-like increase of the reaction rate versus energy is observed.