ATMOSPHERIC TRIATOMIC MOLECULAR STUDIES: THE REPULSIVE $^{4}\Sigma^{-}$ LINEAR PATHWAY FOR THE $O^{1}(^{4}S)+N^{2}(X^{2}\Sigma_{g}^{+})\rightarrow NO^{+}(X^{1}\Sigma^{+})+N(^{4}S)+1.1$ eV $REACTION^{*}$

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1979

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Ohio State University

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A quantitative study has been made of the co-linear $^{4}\Sigma^{-}$ pathway for the state-specific title reaction. A 99 valence configuration MCSCF wavefunction involving the use of doublezeta plus polarization one-electron basis was developed for the long range $^{4}\Sigma^{-}$ state. This long-range $^{4}\Sigma^{-}$ has the character of $0^{+}--N_{2}$ or of $NO^{+}---N$ and is, for most geometries, the $l^{4}\Sigma^{-}$ state. The computed exothemicity is 1.0 eV; this result compares favorably with the experimental value of 1.1 eV. The more sophisticated treatment of the long-range polarization wells provides, as was to be expected, little improvement over the SCF treatment reported $previously.^{1}$ As the system moves from either asymptote along the reaction coordinant to ward the region in which the bond lengths are both comparable to those of $N_{2}0^{+}(X^{2}\Pi)$, the long-range $^{4}\Sigma^{-}$ state has a very repulsive potential -- so repulsive that the surface rises above that of another $^{4}\Sigma^{-}$ state in some regions. Multiple root studies similar to those reported recently for the $^{2}\Sigma^{+}$ states of $HeH_{2}^{+}$ are underway to characterize the avoided $intersection.^{2}$ However, the $^{4}\Sigma^{-}$ state with asymptotic character retains that character every where: only collisions resonant with the potential energy of the crossing relative to the asymptote would have an appreciable chance of making a transition. The barrier and saddle-point region for the co-linear quarter diabatic reaction coordinant have been obtained and will be discussed.

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$^{*}$ Supported in part by the Air Force Office of Scientific Research.$^{1}$ D. G. Hopper, J. Am. Chem. Soc. 100, 1019(1978). $^{2}$ D. G. Hopper, Int. J. Quantum Chem. S12, 305(1978).
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