Predicted thermochemistry and unimolecular kinetics of nitrous sulfide

The geometry of N2S was obtained at the CCSD(T)/aug-cc-pV(T + d)Z level of theory and energies with coupled-cluster single double triple (CCSD(T)) and basis sets up to aug-cc-pV(6 + d)Z. After correction for anharmonic zero-point energy, core-valence correlation, correlation up to CCSDT(Q) and relativistic effects, D-0 for the N-S bond is estimated as 71.9 kJ mol (1), and the corresponding thermochemistry for N2S is Delta H-f(0)degrees = 205.4 kJ mol(-1) and Delta H-f(298)degrees = 202.6 kJ mol(-1) with an uncertainty of +/- 2.5 kJ mol(-1). Using CCSD(T)/aug-cc-pV(T + d) theory the minimum energy crossing point between singlet and triplet potential energy curves is found at r(N-N) approximate to 1.105 angstrom and r(N-S) approximate to 2.232 angstrom, with an energy 72 kJ mol (1) above N-2 + S(P-3). Application of Troe's unimolecular formalism yields the low-pressure-limiting rate constant for dissociation of N2S k(0) = 7.6 x 10(-10) exp(-126 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 700-2000 K. The estimated uncertainty is a factor of 4 arising from unknown parameters for energy transfer between N2S and Ar or N-2 bath gas. The thermochemistry and kinetics were included in a mechanism for CO/H-2/H2S oxidation and the conclusion is that little NO is produced via subsequent chemistry of NNS. (C) 2011 American Institute of Physics. [doi:10.1063/1.3628521]