Relaxation and reaction of HCO and CH/sub 2/(/sup 1/A/sub 1/)

Technical Report · Sat Oct 01 04:00:00 EDT 1983

OSTI ID:5340584

Langford, A O

The laser photolysis/resonance absorption technique has been used to measure absolute rate constants for collisional removal of ground state and vibrationally excited HCO, DCO, and CH/sub 2/ (/sup 1/A/sub 1/). For HCO(0,1,0), rate constants for collisions with He, N/sub 2/, H/sub 2/CO, (HCO)/sub 2/, NO and O/sub 2/ were determined. The number of collisions required to deactivate HCO(0,1,0) ranges from 10 for NO to 10/sup 3/ for N/sub 2/. Upper limits for the rate of reaction between HCO(0,1,0) and NO or O/sub 2/ were established and found to be slower than the corresponding HCO(0,0,0) reaction rate. These results are attributed to the formation of strongly bound collision complexes. This hypothesis is corroborated by inverse kinetic isotope effects which were observed for the ground state reactions. Simple RRKM calculations based on the collision complex mechanism semiquantitatively reproduce the experimental isotope effects as well as the experimentally observed decreases in rate constant which result from vibrational excitation of the HCO or from an increase in temperature. The rate constants for removal of CH/sub 2/ (/sup 1/A/sub 1/) in collisions with He, Ar, Kr, N/sub 2/, CO, O/sub 2/, CH/sub 4/, C/sub 2/H/sub 6/, C/sub 3/H/sub 8/, C/sub 2/H/sub 4/, i-C/sub 4/H/sub 8/, and CH/sub 2/CO were also measured. The number of collisions required to remove CH/sub 2/ (/sup 1/A/sub 1/) ranges from 1 for higher hydrocarbons and CH/sub 2/CO to 10/sup 2/ for He. The relative contributions of reaction and deactivation were not determined. Identical results were found for the (0.1,0) vibrational level which indicates that the collision-induced intersystem crossing rate is independent of the initial vibrational level. Equilibration of the CH/sub 2/ (/sup 1/A/sub 1/) rotational levels in collisions with CH/sub 2/CO and He also found to be very fast with rates factors of 2.7 and 17, respectively, faster than the corresponding removal rates.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5340584
• Report Number(s): LBL-17025; ON: DE84006770
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
640304 -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
ACYL RADICALS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COLLISIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FORMYL RADICALS
ISOTOPE EFFECTS
KINETICS
LASER RADIATION
METHYLENE RADICALS
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATIONS
RADICALS
REACTION KINETICS
RESONANCE ABSORPTION
ROTATIONAL STATES
VIBRATIONAL STATES