The H+N2O -> OH((2)Pi(3/2),v ',N ')+N-2 reaction at 1.5 eV: New evidence for two microscopic mechanisms

The product state-resolved dynamics of the photon-initiated reaction H+N2O- ->OH X ((2)Pi(3/2), upsilon', N') + N-2 has been studied using Doppler-reso lved laser induced fluorescence (LIF) at a mean collision energy of 143 kJ mol(-1) (= 1.48 eV). Nascent OH(upsilon' = 0,1) rovibrational population me asurements indicate that only a small fraction of the available energy is c hanneled into the internal modes of the OH reaction products, as is consist ent with previous work at other collision energies. State-resolved angular scattering distributions have been determined and are found to depend sensi tively on product OH rovibrational quantum state. For the upsilon' = 0 prod ucts, the angular scattering distributions are forward-backward peaking at low N', changing to sideways peaking at high N'. OH products born in the up silon' = 1,N' = 6 state possess forward-backward peaking angular scattering distributions, similar to the OH(upsilon' = 0) products born with intermed iate N'. In addition to these findings, the experiments have allowed the pr ecise determination of the OH quantum state-resolved distributions of kinet ic energy releases and, hence, by energy balance, of internal energies acce ssed in the N-2 co-products. The product state-resolved kinetic energy disp osals are found to broaden somewhat, and to favor higher kinetic energy dis posal, as the internal energy of the OH is increased. The internal energies accessed in the OH and N-2 products are therefore (anti-)correlated. More interestingly, the kinetic energy distributions are bimodal, particularly f or OH(upsilon' = 0) fragments born in high N', and for those born in upsilo n' = 1. This finding is attributed to the operation of two microscopic reac tion mechanisms, which are probably associated with H atom attack at the tw o ends of the NNO target molecule. The results are discussed in the light o f previous experimental and theoretical work. (C) 1999 American Institute o f Physics. [S0021-9606(99)01523-8].