Studies of intramolecular dynamics during unimolecular reactions are important in characterizing the energy transfer into the reaction coordinate responsible for the reactive event. We investigated the dynamics and mode-mode energy transfer immediately prior to the dissociation of hydrazoic acid and hydrogen peroxide. Hydrazoic acid decomposes into NH and N\sb2 when energy is "deposited" in the N-H stretch of the ground electronic state molecule by a pump laser. A specific vibrational motion generates an impulsive energy transfer, which leads to a singlet-triplet transition and subsequent central N-N bond fragmentation. Hydrogen peroxide decomposes into two OH fragments following overtone excitation of an O-H stretch via a specific bending motion capable of producing an impulse of energy flow into the reaction coordinate at the time of the O-O bond dissociation. Modeling the dynamics of overtone-excited HN\sb3, and using an existing model for the dynamics of overtone-excited H\sb2O\sb2, respectively, we first characterize the specificity of the vibrational dynamics preceding the reaction, then establish that these dynamics are stable, that is non-chaotic, and unique in the reaction.