The mechanism of the reaction CH(X 2Π) + N 2 (X 1Σ +g) → HCN (X 1Σ +) + N ( 4S). : II. The intermediate complex region

Abstract

The spin-forbidden reaction CH(X 2Π) + N 2(X 1Σ + g) → HCN (X 1Σ +) + N( 4S) involves a doublet → quartet intersystem crossing. It has been postulated that although the probability for a single pass intersystem crossing is small the existence of a bound intermediate on the lowest doublet potential energy surface increases the overall transition probability by enabling multiple crossings of the doublet—quartet surface intersection. This work considers this proposition, using large scale ((3.2 − 3.8) × 10 6 term), multireference configuration interaction wavefunctions. Two local minima on the lowest doublet potential energy surface are reported, a datively bonded structure N 2 → CH, and a C 2v structure, with HC along the perpendicular bisector of the N 2 bond, which resembles the recently reported geometrical arrangement at the transition state for this reaction, the minimum energy point on doublet—quartet intersection surface. These results enable a clear conceptual picture for the mechanism of this reaction to be presented.