The H+N2O→OH(2Π3/2,v′,N′)+N2 reaction at 1.5 eV: New evidence for two microscopic mechanisms

Abstract

The product state-resolved dynamics of the photon-initiated reaction H+N2O→OH×(2Π3/2,v′,N′)+N2 has been studied using Doppler-resolved laser induced fluorescence (LIF) at a mean collision energy of 143 kJ mol−1 (≡1.48 eV). Nascent OH(v′=0,1) rovibrational population measurements indicate that only a small fraction of the available energy is channeled into the internal modes of the OH reaction products, as is consistent with previous work at other collision energies. State-resolved angular scattering distributions have been determined and are found to depend sensitively on product OH rovibrational quantum state. For the v′=0 products, the angular scattering distributions are forward-backward peaking at low N′, changing to sideways peaking at high N′. OH products born in the v′=1,N′=6 state possess forward-backward peaking angular scattering distributions, similar to the OH(v′=0) products born with intermediate N′. In addition to these findings, the experiments have allowed the precise determination of the OH quantum state-resolved distributions of kinetic energy releases and, hence, by energy balance, of internal energies accessed in the N2 co-products. The product state-resolved kinetic energy disposals are found to broaden somewhat, and to favor higher kinetic energy disposal, as the internal energy of the OH is increased. The internal energies accessed in the OH and N2 products are therefore (anti-)correlated. More interestingly, the kinetic energy distributions are bimodal, particularly for OH(v′=0) fragments born in high N′, and for those born in v′=1. This finding is attributed to the operation of two microscopic reaction mechanisms, which are probably associated with H atom attack at the two ends of the NNO target molecule. The results are discussed in the light of previous experimental and theoretical work.