R. Zils et al., Determination of the equilibrium constant and thermodynamic parameters forthe reaction of pentadienyl radicals with O-2, J PHYS CH A, 105(8), 2001, pp. 1277-1282
The reaction of pentadienyl radicals (C5H7) with O-2 has been studied by a
combination of pulsed laser photolysis and photoionization mass spectrometr
y, These radicals were generated either by the photolysis of 1,3-pentadiene
or by a two step process, photolyzing carbon tetrachloride to form Cl atom
s, which then abstracted a hydrogen atom from 1,4-pentadiene. The equilibri
um between pentadienyl radicals, O-2 and pentadienylperoxy radicals could b
e observed over the temperature range 268-308 K. An analysis of the time-de
pendent signal of pentadienyl radicals was used to evaluate the equilibrium
constant. From the temperature dependence of the equilibrium constant, the
enthalpy change for the reaction C5H7 + O-2 --> C5H7O2 was found to be 56
+/- 5 kJ mol(-1). The C-O bond energy in the C5H7-O-2 adduct is weaker than
those of allyl-type peroxy radicals. Possible values of the heats of forma
tion of C5H7 and C5H7-O-2 radicals and the resonance stabilization energy o
f the C5H7 radical are discussed.