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The D+H2(v=1,j)→HD(v',j')+H reaction. A detailed quasiclassical trajectory study Quasiclassical trajectory calculations of the thermal rate coefficients for the reactions H(D)+O2→OH(D)+O and O+OH(D)→O2+H(D) as a function of temperature A theoretical investigation of the energetics and dynamics of the O(lD) + H, reaction is reported. Two different valence bond diatomics-in-molecules potential energy surfaces were used which differed only in the presence or absence of a small barrier to the C 2, approach. The results of quasi classical trajectory calculations were completely different on the two surfaces and showed that the dynamics of this exothermic reaction are sensitive to features of the surface at large internuclear distances. Reactions were found to occur by two possible mechanisms. In one mechanism, the oxygen atom abstracts a hydrogen atom from the end of the molecule in a direct reaction. Alternatively, the oxygen atom inserts into the H-H bond to form a collision complex which subsequently breaks apart. At all collision energies, the vibrational distribution of products from insertion/decomposition events is statistical while that of abstraction events is centered about v' = 2. An inversion in the total populations of the levels v' = 1 and v' = 2 is observed at a collision energy of 5.0 kcal/ mol-I. Insertion/decomposition reactions lead to hot rotational distributions of products. A transition from cold rotational distributions at low collision energies to a hot distribution at the highest collision energy is observed for abstraction reactions. At low collision energy, the differential cross section for insertion/ decomposition reactions indicates a collision complex is formed whose lifetime is Jess than the rotational period. As the collision energy increases, a transition to the formation of a long-lived complex occurs. 4468

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A semiquantitative calculation is made of the cross section for the quenching of Na(3 2 P) by molecular nitrogen, as a function of initial kinetic energy and of final vibrational quantum number, VI> of the nitrogen molecule. The large observed cross section, which is of gas-kinetic order, can be explained in terms of an intermediate ionic state, involving Na+ and N2-(v=-/L). This state is unstable at infinite separation of Na and N2, but because of the Coulomb attraction it becomes stable at collision distances below about 3 A.As a result of the vibrational structure of both the intermediate and final states, we treat the reaction in terms of a diffusion of the probability flux through a two-dimensional network of potential-energy curves parametrized by both the electronic state and also the vibrational quantum numbers v_ and VI. At each potential-energy curve crossing we compute the transition matrix element for insertion into a Landau-Zener type of transition probability. The transition matrix element is represented as the product of an electronic interaction function (obtained from a correlation, due to Hasted and Chong, of results obtained from charge-transfer processes involving multiply charged ions) and a vibrational overlap integral or Franck-Condon factor. Results are also presented on the quenching of Na(4 2 P) by N2, and on the quenching of Na(3 2 P) by CO. All the results have the same general character: The total cross section is of gas-kinetic order and depends only weakly on kinetic energy. The partial cross sections for excitation of the different final vibrational levels V/ show a rather broad distribution, with somewhat more than half the energy of electronic excitation ending up as vibrational excitation.

As an extension of earlier work on the quenching of electronically excited alkali metal atoms by N2 and CO, that uses a model of curve crossing involving an ionic intermediate state, here we treat the quenching of O(1D) by N2, a process which proceeds by curve crossing of covalent states. The model is also applied to the vibrational relaxation of N2 in collision with O(3P) atoms and to the unimolecular decomposition of N2O. The order of magnitude of the rate constants for all three processes can be explained by the present model, using the same value of the electronic coupling potential for the curve-crossing process; this value is significantly larger than the corresponding value for isolated O(3P) and O(1D) atoms. In the quenching of O(1D) by N2, the electronic-vibrational coupling is weak, channeling less than 5% of the electronic quantum into vibrational levels of N2, but the quenchant N2 is likely to be rotationally excited. The vibrational relaxation of N2 by oxygen atoms arising due to curve crossing rather than to adiabatic (Landau-Teller) collisions has a significant activation energy, ∼0.8 eV, so that the rate coefficient for vibrational relaxation due to curve crossing is expected to show a strong temperature dependence and to dominate at temperatures above 600°K.