Knowledge Bank

A quantitative study has been made of the co-linear $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ state. This long-range $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ has the character of $0+--N2$ or of $NO+---N$ and is, for most geometries, the $l4\Sigma -$ 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 $N20+(X2\Pi )$, the long-range $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ state has a very repulsive potential -- so repulsive that the surface rises above that of another $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ state in some regions. Multiple root studies similar to those reported recently for the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +$ states of $HeH2+$ are underway to characterize the avoided $intersection.2$ However, the $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ 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.