Vd. Knyazev et Ir. Slagle, THERMOCHEMISTRY AND KINETICS OF THE REACTION OF 1-METHYLALLYL RADICALS WITH MOLECULAR-OXYGEN, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 102(45), 1998, pp. 8932-8940
The kinetics of the reaction CH3CHCHCH2 + O-2 reversible arrow CH3CHCH
CH2O2 has been studied using laser photolysis/ photoionization mass sp
ectrometry. Room-temperature decay constants of the CH3CHCHCH2 radical
were determined in time-resolved experiments as a function of bath ga
s density ([He] (3-24) x 10(16) molecule cm(-3). The rate constants ar
e in the falloff region under the conditions of the experiments. Relax
ation to equilibrium in the addition step of the reaction was monitore
d within the temperature range 345-390 K. Equilibrium constants were d
etermined as a function of temperature and used to obtain the enthalpy
of reaction 1. At high temperatures (600-700 K), no reaction of CH3CH
CHCH2 with molecular oxygen could be observed and upper limits to the
rate constants were determined (1 x 10(-16) cm(3) molecule(-1) s(-1) a
t 600 K and 2 x 10(-16) cm(3) molecule(-1) s(-1) at 700 K). Structures
, vibrational frequencies, and energies of several conformations of CH
3CHCHCH2, CH3CHCHCH2O2, and CH3CH(OO)CHCH2 were calculated using ab in
itio UHF and MP2 methods. The results were used to calculate the entro
py changes of the addition reaction. These entropy changes combined wi
th the experimentally determined equilibrium constants resulted in the
average R-O-2 bond energy for terminal and nonterminal addition: Delt
a H-298(0) = 82.6 +/- 5.3 kJ mol(-1). Earlier experimental results on
the kinetics of relaxation to equilibrium in the reaction of allyl rad
ical with O-2 are reanalyzed using an improved kinetic mechanism which
accounts for heterogeneous wall decay of the CH2CHCH2O2 adduct. The c
orrected value of the CH2CHCH2-O-2 bond energy (77.0 kJ mol(-1)) is de
termined from the reinterpreted data.