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.
The rate constant for the C6H5 +
H2 → C6H6 + H reaction has been
measured by pyrolysis/Fourier transform
infrared spectrometry (P/FTIRS) in the temperature range of 548−607 K
and by pulsed-laser photolysis/mass spectrometry (PLP/MS) in the temperature range of 701−1017 K.
By P/FTIRS, the reaction was studied
by measuring time-resolved concentration profiles of the reactant
(C6H5NO) and the product
(C6H6) using
highly diluted mixtures of C6H5NO in
H2 (with or without Ar dilution). In PLP/MS
experiments, the C6H5
radical was generated by the photolysis of
C6H5COCH3 at 193 nm in the
presence of several Torr of H2. The
C6H5 + H2 rate constant was
determined by the absolute yields of C6H6 and
C6H5CH3 products. The
results
of these two spectrometric measurements agree closely with our
theoretically predicted expression, k = 5.72
× 104
T
2.43 exp
(−3159/T) cm3/(mol·s) and with that of a
shock-tube study by Troe and co-workers (ref )
in the temperature range of 1050−1450 K. Preliminary kinetic
data on the CH3 + C6H5
association reaction
are also presented.
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