The product state-resolved dynamics of the photon-initiated reaction HϩN 2 O→OH ϫ( 2 ⌸ 3/2 ,vЈ,NЈ)ϩN 2 has been studied using Doppler-resolved laser induced fluorescence ͑LIF͒ at a mean collision energy of 143 kJ mol Ϫ1 ͑ϵ1.48 eV͒. Nascent OH(vЈϭ0,1) 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 vЈϭ0 products, the angular scattering distributions are forward-backward peaking at low NЈ, changing to sideways peaking at high NЈ. OH products born in the vЈϭ1,NЈϭ6 state possess forward-backward peaking angular scattering distributions, similar to the OH(vЈϭ0) products born with intermediate NЈ. 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 N 2 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 N 2 products are therefore ͑anti-͒correlated. More interestingly, the kinetic energy distributions are bimodal, particularly for OH(vЈϭ0) fragments born in high NЈ, and for those born in vЈϭ1. 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.

The rotational angular momentum orientation and alignment of the NO fragments generated via linearly polarized 308 nm photodissociation of NO2 has been determined using laser induced fluorescence. By observing the dependence of the photofragment NO Doppler-resolved transition line shapes on experimental geometry, it has proved possible to determine multipole moments of the photofragment angular momentum distribution up to, and including, rank 3. The implications of the results for the mechanism of the dissociation are considered.

OH(OD) quantum state populations, rovibrational quantum state-resolved center-of-mass angular scattering distributions, and H2(HD) coproduct internal energy release distributions have been determined for the hot H atom reactions with H2O and D2O at mean collision energies close to 1.4 eV. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the radical products. The OH(2Π1/2,v′=0,N′=1,A′) and OD(2Π1/2,v′=0,N′=1,A′) angular distributions generated by the two isotopic reactions are quite distinct: that for the reaction with H2O shows intensity over a wide range of center-of-mass scattering angles, and peaks in the sideways direction, while the state-resolved angular distribution for the reaction with D2O displays more scattering in the backward hemisphere. For higher OH(OD) angular momentum states the differences in the angular distributions for the two reactions are less marked, with both systems showing a slight preference for backward scattering. The kinetic energy release distributions are insensitive to OH(OD) quantum state and to isotopic substitution, and reveal that the H2(HD) coproducts are born internally cold at 1.4 eV. OH(OD) quantum state averaged energy disposals in the two reactions are also presented. The new experiments provide detailed mechanistic information about the two reactions and clarify the dominant sources of product OH(OD) rotational excitation. Current theoretical understanding of the reaction is critically assessed.

The title reaction has been studied both experimentally and computationally at a mean collision energy of 2.48 eV. OD quantum state populations, rotational alignment parameters, rovibrational quantum state-resolved center-of-mass angular scattering distributions and HD co-product internal energy release distributions have been determined, along with OD quantum state averaged energy disposals. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the radical products. The OD angular scattering distributions show a preference for scattering in the forward direction, and are quite different from those observed previously at the lower collision energy of 1.4 eV. So too are the kinetic energy release distributions, which reveal that the HD co-products are born significantly more internally excited at 2.48 eV than at 1.4 eV. The HD internal energy distributions obtained from analysis of the Doppler resolved profiles are in reasonable accord with that derived from the direct HD population measurements performed by Zare and co-workers ͓J. Chem. Phys. 98, 4636 ͑1993͔͒ at collision energies around 2.7 eV. The data are compared in detail with the results of new quasi-classical trajectory ͑QCT͒ calculations employing two alternative potential energy surfaces ͑PESs͒, as well as with the results from previous QCT studies of the title reaction by other workers. Refinements to the most recent of the PESs employed here, that developed using the iterative methods of Collins and Zhang and co-workers ͓J. Chem. Phys. 115, 174 ͑2001͔͒, are also described. The theoretical results obtained using this refined PES agree very well with many of the experimental observables, and the surface appears to be a significant improvement on those previously developed. However, even with this new PES, the QCT calculations at 2.48 eV overestimate the internal excitation of the HD products.

The absolute value of the cross section for the abstraction reaction between fast H atoms and H2O has been determined experimentally at a mean collision energy of 2.46 eV. The OH population distribution at the same mean energy has also been determined. The new measurements are compared with state-of-the-art quantum mechanical and quasiclassical scattering calculations on the most recently developed potential energy surface.