The rate constants for the reactions of C2H4and NH3are determined by termination of the reactions in the gas phase after different times of reaction. The average value for the rate constant of the N atom–C2H4reaction at 150 °C is 1.8 × 1010 cc mole−1sec−1, when the initial N-atom concentration is determined from the maximum production of HCN. The average value for the rate constant for the over-all reaction of NH3with excited nitrogen molecules, at 104 °C in the "poisoned" system, and 83 °C in the "unpoisoned" system, for low initial flow rates of NH3, or short reaction time, is 2.2 × 1010 cc mole−1sec−1. The decrease in value of this rate constant at higher initial flow rates of NH3and longer reaction times in the "poisoned" system indicates that the species responsible for NH3decomposition is generated during the decay of N atoms in the presence of NH3. The value for the NH3reaction is discussed in terms of energy transfer.