A THEORETICAL TREATMENT OF THE INTERSYSTEM CROSSING IN THE SPIN-FORBIDDEN REACTION NO(X2II) + CO(X1SIGMA +) N(4S) + CO2(X1SIGMA G+)

The mechanism of the spin-forbidden reaction NO(X2Π)+CO(X1Σ+)→N(4S)+CO2(X1Σ+g) is considered. Two minimum energy points on the doublet–quartet crossing surface are reported using multireference configuration interaction (MRCI) wavefunctions. The lowest-energy crossing point has an approximate C2v structure resembling the products N+CO2. This region lies 60 kcal/mol above the reactant channel, suggesting that the title reaction would not occur under typical combustion conditions. A higher-energy point with a linear structure is also located. Two local minima on the lowest 2A″ potential energy surface are reported at the QCISD and MRCI levels.