Kinetic and theoretical investigations of the S + NO 2 reaction

Ground state atomic sulfur was generated by 193‐nm laser photolysis of CS 2 precursor in Ar bath gas, in the presence of a large excess of NO 2 under pseudo‐first‐order conditions. Decays of S( 3 P J ) were monitored over 292–656 K and pressures of 14–535 mbar. No pressure dependence was observed, and the second‐order constants are summarized as k ( T ) = 1.9 × 10 −11 exp(+4.1 kJ mol −1 )/ RT cm 3 molecule −1 s −1 , with a 95% confidence interval of ±7%. The potential energy surfaces for SNO 2 and S(NO 2 ) 2 were explored using QCISD/6‐311G(d,p) theory for geometries and frequencies, followed by single‐point calculations based on coupled‐cluster theory and extrapolation of results with cc‐pV(T+d)Z and cc‐pV(Q+d)Z basis sets to the complete basis set limit. Corrections were made for scalar relativistic effects and core–valence correlation. A mechanism involving initial barrierless addition of S to the N atom in NO 2 , followed by fast dissociation to SO + NO, is consistent with the observed lack of pressure dependence and a Rice–Ramsperger–Kassel–Marcus estimate of the dissociation rate of SNO 2 compared to collisional stabilization. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 90–99, 2012