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We report a new calculation of the N+O2 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of NO2 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the O1s and N1s electrons with a cc-pVQZ basis set. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The convergence of the barrier height for the O+H2→OH+H reaction has been studied as a function of the size of the active space and basis set completeness. The barrier height is rapidly convergent with respect to expansion of the active space. Addition of 2p→2p’ correlation terms to the active space lowers the barrier to the O+H2 reaction by about 2.0 kcal/mol, but addition of 3d and other terms has little additional effect. Multireference singles and doubles contracted CI plus Davidson’s correction calculations using a [5s5p3d2f1g/4s3p2d1f] basis set with a 5σ2π active space lead to a barrier height of 12.7 kcal/mol. Including an estimate of the CI contraction error and basis set superposition error leads to 12.4 kcal/mol as the best estimate of the barrier height. [ABSTRACT FROM AUTHOR]

We present global ab initio potential energy surfaces for the three lowest energy 1A’, 3A‘, and 1A‘ surfaces of HNO. These surfaces are the lowest three states of the HNO and HON molecules, and they correlate to the ground electronic states of H+NO and O+NH. In addition, the 3A‘ surface correlates to the ground state of N+OH. The surfaces are based on approximately 800 ab initio calculations that were done using an internally contracted multireference configuration interaction calculation with a large basis set. The ab initio points were fit to a combination of Morse and spline functions in each of the three possible Jacobi coordinates, and the resulting splines were smoothly switched together, and combined with other functions to yield globally defined potentials. Properties of the HNO and HON minima and dissociation energies on these potentials are in good agreement with previous high quality calculations. The N+OH and O+NH reactions are found to have no barriers to formation of HON or HNO, respectively. Isomerization of HON to HNO involves barriers that are higher than the HON dissociation barrier on the singlet surfaces but not on the triplet surface. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a quasiclassical trajectory study of the collisions which occur on the 1A’, 3A‘, and 1A‘ potential surfaces of HNO using recently developed global potential surfaces that were derived from ab initio calculations. Each of these surfaces was assumed to be uncoupled from the other surfaces for the purposes of the calculations, and the appropriate statistical average of electronic states for each process was calculated. For N+OH and O+NH, we specifically studied reactive collisions which give H+NO as products, and we also studied the production of N+OH from O+NH. Overall rate constants calculated for either N+OH or O+NH are in good agreement with most experiments, and in addition, the product NO vibrational distribution from the N+OH reaction is in good correspondence with recent measurements, revealing modest excitation that is close to what would be expected from a statistical distribution. For O+NH, the calculated NO vibrational distributions are much hotter than statistical, in apparent disagreement with recent measurements. However, a careful analysis of limitations on the measurements due to spectral interference and to collisional relaxation indicates that it is not possible to say if theory and experiment are at odds for this reaction. We find a significant cross section for O+NH→N+OH on the 3A‘ surface (roughly 5% of the total reactive cross section, independent of energy), and this leads to rate constants at low temperatures that are orders of magnitude higher at low temperature than estimates made earlier based on H atom abstraction on the 5Π surface.The mechanism of this reaction is found to involve three steps: addition to form HNO, isomerization to HON, and dissociation to produce N+OH. We have also studied nonreactive vibrational and rotational excitation in H+NO collisions, and we obtain distributions that are somewhat closer to experiment than obtained in previous theoretical studies, although... [ABSTRACT FROM AUTHOR]

We have studied the reaction of N and O atoms with a (9,0) carbon nanotube using clusters and the ONIOM method with the B3LYP/6-31G* level of theory. For both N and O atoms in their ground state, addition to the CNT requires a surface crossing and presumably involves a barrier, while we show that addition of the excited state of N(2D) has no barrier, and we believe this also to be true for O(1D). Both N and O atoms bond in a bridged structure and have bond strengths of 25.0 and 67.9 kcal/mol (estimated), respectively, with respect to CNT plus the ground state of the N or O atom. [Copyright &y& Elsevier]