The influence of vibrational excitation on the decay rate of NH2radicals in the presence of selected substrates has been studied using the laserhyphen;induced fluorescence (LIF) technique. The NH2radicals were generated by infrared multiple photon dissociation (IRMPD) of selected precursors (N2H4, CH3NH2), and the state selected NH2(vPrime;2=0,1) decay was observed by means of the sensitive LIF measurement of lsqb;NH2rsqb;. The reactions studied were of the type: NH2(vrsqb;2=0,1)+Rrarr;products, with R=NO, CH3NH2, N2H4. The reaction rates were determined under pseudohyphen;firsthyphen;order conditions, and were found to be strongly dependent on the vibrational state of the NH2radical, e.g.,kNO(vPrime;2=0)=1.4times;10minus;11cm3thinsp;moleculeminus;1thinsp;sminus;1andkNO(vrsqb;2=1)=3.2times;10minus;11cm3thinsp;moleculeminus;1thinsp;sminus;1. This influence of vibrational excitation on the total decay rates is discussed and compared with previously reported data on thermal excitation. In thermal studies of these same chemical reactions, a negative temperature coefficient was found for the reaction rate constants. The contribution of diffusion and of vibrational relaxation processes is also considered, as well as the relative importance of the twohyphen;body vs the threehyphen;body collision reaction channels: NH2+NH2rarr;NH3+NH and NH2+NH2+Mrarr;N2H4+M for M=O2, N2, and Ar.
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