An experimental and theoretical study of degradation pathways for atmospheric halocarbons
The issue of ozone depletion by chlorofluorocarbons (CFCs) is of great current concern. UV photodissociation of CFCs in the stratosphere produces a chlorine atom and a trihalomethyl radical. While the catalytic role of atomic chlorine in ozone depletion processes has been well studied, the part played by the other fragment of the dissociation remains largely unknown. Two possible catalytic cycles initiated by CX3 (X = F, Cl) have been proposed, in which CX3O and CX3O2 are the key species to understand these cycles. The dissociation pathway of CX3O radicals have been studied using Hartree-Fock theory, Moller-Plesset and spin projection correlation methods. The dissociation barrier heights and the heat of reaction for these processes have been determined. CF3O has received extensive study both theoretically (using ab initio theory) and experimentally (using laser-induced fluorescence technique). The experimental observations for CF3O are consistent with the theoretical predictions. A detailed theoretical study has been carried out on dissociation pathways of carbonyl halides resulting from the degradation of CX3O radicals, and on the molecular properties of some electronic excited states of CF2O using ab initio theory. The study on the dissociation barrier heights for carbonyl halides suggests that chlorofluoromethane with less than two fluorine atoms degrades to carbon monoxide; those with at least two fluorine atoms yield carbon dioxide in the stratosphere. The laser photolysis/infrared chemiluminescence technique has been applied to the kinetic study of the reaction of CF(3) with NO2. The absolute reaction rate constant was measured at 300 plus or minus 4 K to be (2.5 plus or minus 0.4) x 10(exp -11) cu cm molecule(exp -1) s(exp -1) from monitoring the rise time of CF2O time-resolved vibrational fluorescence.
- Research Organization:
- Wayne State Univ., Detroit, MI (United States)
- OSTI ID:
- 6764920
- Country of Publication:
- United States
- Language:
- English
Similar Records
Dissociation pathways of carbonyl halides
Dissociation dynamics of perhaloalkoxy radicals
Related Subjects
540120* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
AIR POLLUTION
ATMOSPHERIC CHEMISTRY
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON MONOXIDE
CARBON OXIDES
CARBONYLS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMILUMINESCENCE
CHEMISTRY
CHLOROFLUOROCARBONS
DISSOCIATION
EARTH ATMOSPHERE
ELECTROMAGNETIC RADIATION
ENERGY-LEVEL TRANSITIONS
EXCITATION
HALIDES
HALOGEN COMPOUNDS
KINETICS
LUMINESCENCE
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
OZONE
POLLUTION
RADIATIONS
RADICALS
REACTION KINETICS
STRATOSPHERE
ULTRAVIOLET RADIATION