KINETICS AND PRODUCTS OF THE REACTION SO3-2(NH3+N)

The kinetics of the gas phase reaction SO3 + NH3 + M were measured in N-2 at 295 K over the pressure range 10-400 Torr with laminar flow rea ctors coupled to a chemical ionization mass spectrometer. The pressure dependence of the second-order rate coefficient is fit well by the ge neralized Troe formalism giving k(0) = (3.9 +/- 0.8) x 10(-30) cm(6) m olecule(-2) s(-1) and k(infinity) = (4.7 +/- 1.3) x 10(-11) cm(3) mole cule(-1) s(-1). The association product of the SO3 + NH3 reaction and secondary acid cluster products were detected by chemical ionization m ass spectrometry. Models of the temporal behavior of SO3, sulfamic aci d, and sulfamic acid dimer show that sulfamic acid dimerizes at near t he hard sphere gas kinetic limit (k > 5 x 10(-11) cm(3) molecule(-1) s (-1), 20 Torr N-2, 295 K) and the dimer is relatively stable with resp ect to decomposition to monomers (Delta G degrees(298) less than or eq ual to -9 kcal mol(-1)).