The errors
reflect an estimated 20% uncertainty in the measured rate
coefficients. The fit results changed by less than 10% for 0 <
m < 3. The assumption that the high-pressure limiting rate
coefficient is independent of temperature (i.e. m = 0) is
reasonable considering that the high-pressure limit rate coefficient
is large at room temperature and the temperature
dependence of k∞ is generally weak (see, for example, ref 10).
At temperatures above 380 K the unimolecular decomposition
of H3NSO3 into SO3 + NH3 competed efficiently with the
association reaction, and the SO3 decays were not simple
exponentials (see Figure 2). For these conditions the SO3 decay
and H3NSO3 appearance were modeled to extract the rate
coefficient for decomposition of H3NSO3. The kinetics were
modeled with the following mechanism