E.s.r. studies of the reactions of atomic oxygen and hydrogen with simple hydrocarbons

Authors:
  • JBJ. M. Brown
    J. M. Brown
  • BTB. A. Thrush
    B. A. Thrush
Publisher website
Google Scholar
Abstract
Electron spin resonance has been used to study the reaction of oxygen atoms in a nitrogen carrier and of hydrogen atoms in an argon carrier with simple hydrocarbons in a fast flow system at total pressures around 2 mm Hg. The reaction between oxygen atoms and acetylene occurs predominantly by the mechanism: O+C2H2= CH2+CO (3) O+CH2= CO+2H (6) CH2+C2H2= C3H4(12) where k3=(9.2 ± 0.4)× 1010 cm3 mole–1 sec–1 and k6=(2.7 ± 1.0)k12 both at 298°K. The initial step in the reaction of oxygen atoms with methyl acetylene is O+CH3 . C CH = CH3 . CH : + CO (13) with k13=(4 ± 1)× 1011 cm3 mole–1 sec–1 at 298°K; the total rate constant for the disappearance of oxygen atoms being 3–4 times greater. The mechanisms of the O+C2H4 and O+CH4 reactions have been deduced from their overall stoichiometries and the hydrogen atom yields. For the initial steps O+C2H4= CH3+HCO (15) O+CH4= CH3+OH (23)k15=(3.2 ± 0.4)× 1011 cm3 mole–1 sec–1 at 298°K and k23=(7 ± 2)× 1012 exp (–7700 ± 300/RT) cm3 mole–1 sec–1 between 450 and 600°K. The addition of hydrogen atoms to methyl acetylene and to ethylene were second order processes, H+C3H4= C3H5(4) H+C2H4= C2H5(17) with k4=(2.4 ± 0.3)× 1011 cm3 mole–1 sec–1 and k17=(8.8 ± 0.4)× 1010 cm3 mole–1 sec–1 at 298°K.