An ab Initio Excursion on the Lowest 18 Electronic Surfaces of the NCl + NCl System: Some Insight into the Long-Range Self-Quenching Pathways of the First Excited State of NCl

Abstract

A series of state-averaged complete active space self-consistent field (SA-CASSCF) computations were carried out in search of low-energy self-annihilation pathways for two NCl molecules in their first excited state (a'A).Numerous scans of the lowest 18 electronic surfaces that correlate with the interaction of two NCI molecules in the X 3 Σ - , a'A, and b 1 Σ + states are reported. Eight long-range, low-energy pathways were located (four in C 2 v and eight in C 2 h symmetry) that connect NCl(a 1 Δ) + NCl(a 1 Δ) to NCl(X 3 Σ - ) + NCl(b 1 Σ + ) and NCl(X 3 Σ - ) + NCl(a 1 Δ). It was possible to rigorously characterize the minima on four of these seams of crossings (MSXs). The MSXs between the a + a manifold and the X + b manifold are only 1.8-4.5 kcal mol - 1 above the a + a asymptote and therefore energetically accessible. Additional scans suggest these MSXs are planar but, to some extent, prefer to distort from C 2 v cis and C 2 h trans structures to C, orientations, which would lower the MSX energies slightly.