Pressure and temperature dependence of the OH+C/sub 2/H/sub 2/ reaction above 800 K

Journal Article · Sat Sep 15 04:00:00 EDT 1984 · J. Chem. Phys.; (United States)

OSTI ID:6548432

Smith, G P; Fairchild, P W; Crosley, D R

The rate constant for the reaction OH+C/sub 2/H/sub 2/ has been measured at 900, 1100, and 1300 K. The experimental method was that of laser pyrolysis/laser fluorescence, in which a pulsed CO/sub 2/ laser heats a mixture of SF/sub 6/, N/sub 2/, H/sub 2/O/sub 2/, and C/sub 2/H/sub 2/. The rate constant is determined from the rate of decay of laser-induced fluorescence signals in OH, formed by pyrolysis of the peroxide and consumed by reaction with the acetylene. At the two higher temperatures the rate constant is independent of pressure between 10 and 120 Torr but at 900 K it was observed to be pressure dependent over a similar range. The rate constant at 1100 K is 2.7 +- 0.6 x 10/sup -3/ cm/sup 3/ s/sup -1/, and rises to 5.8 +- 0.8 x 10/sup -13/ cm/sup 3/ s/sup -1/ at 1300 K. Calculations of the temperature and pressure dependence of the addition channel OH+C/sub 2/H/sub 2/+M..-->..C/sub 2/H/sub 2/OH+M were made using Troe's approach, based on flow tube data at a lower temperature. These theoretical calculations are consistent with the present results as well as previous experimental measurements, showing a decrease in the importance of the addition channel with increasing temperature and the onset of a direct route in the region of 1000 K. These considerations of combined pressure and temperature dependence of reaction rates, and changes in mechanism, must be properly taken into account in detailed combustion chemistry models which cover a large range in temperature and pressure.

• Research Organization: Chemical Physics Laboratory, SRI International, Menlo Park, California 94025
• OSTI ID: 6548432
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 81:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACETYLENE
ALKYNES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMBUSTION
DECOMPOSITION
ELECTROMAGNETIC RADIATION
HIGH TEMPERATURE
HYDROCARBONS
HYDROXYL RADICALS
KINETICS
LASER RADIATION
ORGANIC COMPOUNDS
OXIDATION
PRESSURE DEPENDENCE
PYROLYSIS
RADIATIONS
RADICALS
REACTION KINETICS
SOOT
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
VERY HIGH TEMPERATURE