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Notes: The product-state-resolved dynamics of the reaction H+CO2→OH(2Π;ν,N,Ω,f)+CO have been explored in the gas phase at 298 K and center-of-mass collision energies of 2.5 and 1.8 eV (respectively, 241 and 174 kJ mol−1), using photon initiation coupled with Doppler-resolved laser-induced fluorescence detection. A broad range of quantum-state-resolved differential cross sections (DCSs) and correlated product kinetic energy distributions have been measured to explore their sensitivity to spin–orbit, Λ-doublet, rotational and vibrational state selection in the scattered OH. The new measurements reveal a rich dynamical picture. The channels leading to OH(Ω,N∼1) are remarkably sensitive to the choice of spin–orbit state: Those accessing the lower state, Ω=3/2, display near-symmetric forward–backward DCSs consistent with the intermediacy of a short-lived, rotating HOCO (X˜ 2A′) collision complex, but those accessing the excited spin–orbit state, Ω=1/2, are strongly focused backwards at the higher collision energy, indicating an alternative, near-direct microscopic pathway proceeding via an excited potential energy surface. The new results offer a new way of reconciling the conflicting results of earlier ultrafast kinetic studies. At the higher collision energy, the state-resolved DCSs for the channels leading to OH(Ω,N∼5–11) shift from forward–backward symmetric toward sideways–forward scattering, a behavior which resembles that found for the analogous reaction of fast H atoms with N2O. The correlated product kinetic energy distributions also bear a similarity to the H/N2O reaction; on average, 40% of the available energy is concentrated in rotation and/or vibration in the scattered CO, somewhat less than predicted by a phase space theory calculation. At the lower collision energy the discrepancy is much greater, and the fraction of internal excitation in the CO falls closer to 30%. All the results are consistent with a dynamical model involving short-lived collision complexes with mean lifetimes comparable with or somewhat shorter than their mean rotational periods. The analysis suggests a potential new stereodynamical strategy, "freeze-frame imaging," through which the "chemical shape" of the target CO2 molecule might be viewed via the measurement of product DCSs in the low temperature environment of a supersonic molecular beam. © 2000 American Institute of Physics.

Notes: The quantum state resolved rotational angular momentum alignments of the OH products of the H+CO2 reaction have been determined for a range of states spanning those most populated by reaction at a collision energy of 2.5 eV. Surprisingly, for all quantum states studied, the angular momentum is shown to be aligned preferentially in the scattering plane, containing the reagent and product relative velocity vectors. The data suggest that out-of-plane HO–CO torsional forces play a significant role in dissociation of the HOCO intermediate. The polarization behavior mirrors observed in the isoelectronic H+N2O reaction [see the accompanying paper, J. Chem. Phys. 113, 3162 (2000)], and the data are compared with those obtained for that system, and with previous theoretical and experimental work on this important reaction. © 2000 American Institute of Physics.

Notes: The reaction Ba+HI→BaI(v)+H was studied under beam-gas, single-collision conditions with an average center-of-mass collision energy of 13 kJ mol−1. BaI (v) rotational distributions were recorded for v=0, 4, 8, 12, 16, and 18 by means of selectively detected laser-induced fluorescence of the BaI C 2Π–X 2Σ+ band system. Each rotational distribution exhibits a maximum toward its high energy end and the range of rotational states becomes narrower as product vibration increases. Because the kinematic constraint causes almost all reagent orbital angular momentum to appear in product rotation, the principle of angular momentum conservation provides the means for determining specific opacity functions from the rotational distributions and the reagent relative velocity distribution. The specific opacity functions are narrow functions of the impact parameter. The peak values decrease smoothly from approximately 4.5 A(ring) for v=0 to 1.5 A(ring) for v=18, indicating a strong correlation between impact parameter and product vibrational state such that Ba+HI collisions with small impact parameter produce BaI with large vibrational excitation.