Reaction kinetics of the addition of atomic sulfur to nitric oxide

The reaction of S(3PJ) with NO (2Π) in an Ar bath gas has been studied by the laser photolysis-resonance fluorescence technique over 300-810 K at pressures from 60 to 800 mbar. The observed second-order rate constants are close to the low-pressure limit. Fitting of Troe's formalism to experiment, with an estimated Fcent=0.78 exp(-T/7445) and k∞ given subsequently, yields k0=(6.2±0.6)x10-33 exp(+(940±40)/T) cm6 molecule-2 s-1. Error limits are ±25%. A theoretical analysis of this value suggests that the average energy transferred during collisions between Ar and the excited intermediate is <ΔE>=-360-160+90 cm-1. Over 300-800 K, the high-pressure limit is predicted to be k∞=2.2x10-10 (T/300)0.24 cm3 molecule-1 s-1. Doublet and quartet adducts between S and NO were characterized via CBS-QB3 theory. The kinetic data can be rationalized with SNO (2A') as the major product, and an ab initio estimate of ΔfH298 for SNO is 176±8 kJ mol-1