Ab Initio Calculation of Potential Energy Curves for the Ion Molecule Reaction O++N2 → NO+ + N

Abstract

Configuration interaction calculations verified an earlier hypothesis that the experimentally observed apparently anomalous behavior of the O++N2 → NO+ + N reaction is due to the symmetry and spin restrictions which prohibit the ground state reactants or products from correlating directly with the ground state intermediate. Complex symmetry adapted functions were used, and all single and double excitations were included for the ground and first excited Πi2 states, the lowest and second 2Σ+ states, the Π4 state and the 4Σ- state of the intermediate NNO+ for two cuts through the potential surface close to the reaction path. The number of configurations included were: Πi2 (123), 2Σ+ (177), 4Π (1349) and 4Σ- (1310). Analyses of the first order CI density matrices at large distances in terms of their ``fragmental'' MO's (or AO's) verified that the 4Σ- NNO+ state was formed from the ground state reactants O+(4Su) + N2(1Σg+) and that it separated into ground state products NO+(1Σ+) + N(4Su). The positions of other electronic states of NNO+ were well substantiated in agreement with photoelectron spectroscopic measurements. The calculated potential energy curves show an even greater wealth of structure than would have been anticipated prior to such a detailed computation. The most significant conclusion of the present research is the unambiguous confirmation of the overriding role that spin and symmetry restrictions play in any type of collisional process.