Experimental rate measurements for NS + NO, O2 and NO2, and electronic structure calculations of the reaction paths for NS + NO2

This study reports the first direct kinetic measurements on the NS radical. NS was produced by photolysis of N4S4 at 248 nm and was detected via laser-induced fluorescence. A fast reaction was observed between NS and NO2, with k = (2.54 ± 0.12) × 10-11 cm3 molecules-1 s-1 (error = 2σ including systematic errors) at 295 K. The rate coefficient shows a small negative temperature dependence over the range 295-673 K, which is represented by k = (2.57 ± 0.11) × 10-11(T/295 K)-1.10±0.10 cm3 molecule-1 s-1. The reaction was also investigated using density functional theory (B3LYP/6-31G**) to calculate the geometries of the stationary points on the potential energy surface, coupled with Brueckner doubles and perturbative triples to determine energy differences. The calculations show a direct route from reactants to N2 + SO2, via a series of isomers of NSNO2, with no energy barrier higher than that of the entrance channel. It is also possible that the reaction forms SNO + NO; this channel has a higher barrier than that found on the N2 + SO2 route, which is also below the entrance channel, but involves fewer isomerizations. No reaction was observed between NS and O2 or NO, at temperatures up to 623 K and upper limits of 1 × 10-15 and 3 × 10-14 cm3 molecule-1 s-1, respectively, were placed on these rate coefficients.