The unimolecular decomposition of nitrosobenzene has been studied
at 553−648 K with and without added
NO under atmospheric pressure. Kinetic modeling of the measured
C6H5NO decay rates by including
the
rapid reverse reaction and minor secondary processes yielded the
high-pressure first-order rate constant for
the decomposition C6H5NO →
C6H5 + NO (1),
= (1.42 ± 0.13) × 1017 exp [−(55 060 ±
1080)/RT] s-1,
where the activation energy is given in units of cal/mol. With the
thermodynamics third-law method, employing
the values of
and those of the reverse rate constant measured in our earlier study by
the cavity ring-down
technique between 298 and 500 K, we obtained the C−N bond
dissociation energy, D°0
(C6H5−NO) = 54.2
kcal/mol at 0 K, with an estimated error of ±0.5 kcal/mol. This
new, larger bond dissociation energy is fully
consistent with the quantum mechanically predicted value of 53.8−55.4
kcal/mol using a modified Gaussian-2
method. Our high-pressure rate constant was shown to be consistent
with those reported recently by Horn et
al. (ref ) for both forward and reverse reactions after proper
correction for the pressure falloff effect.