Pressure and temperature dependence of the rate constants for the association reactions of CH radicals with CO and N2 between 202 and 584 K

Brownsword, Richard A.; Herbert, Lee B.; Smith, Ian W. M.; Stewart, David W.

doi:10.1039/ft9969201087

Cited by 29 publications

(51 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The addition reaction is apparently fast, even at low temperatures (Le , which suggests that the reaction has no kinetic barrier. The third-order rate constant was found to be k 0 = (5.7 -0.30) · 10 -30 cm 6 s -1 at 53 K (Le , with similar values at room temperature (Becker et al, 1996;Brownsword et al, 1996).…”

Section: Figmentioning

confidence: 94%

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

et al. 2012

View full text Add to dashboard Cite

Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (k < 120 nm) or magnetospheric electrons in the outer reaches of the atmosphere. Far UV radiation (120-200 nm), which is transmitted down to the stratosphere of Titan, is expected to affect hydrocarbon chemistry only and not initiate the formation of nitrogenated species. We examined the chemical properties of photochemical aerosol produced at far UV wavelengths, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which allows for elemental analysis of particle-phase products. Our results show that aerosol formed from CH 4 /N 2 photochemistry contains a surprising amount of nitrogen, up to 16% by mass, a result of photolysis in the far UV. The proportion of nitrogenated organics to hydrocarbon species is shown to be correlated with that of N 2 in the irradiated gas. The aerosol mass greatly decreases when N 2 is removed, which indicates that N 2 plays a major role in aerosol production. Because direct dissociation of N 2 is highly improbable given the immeasurably low cross section at the wavelengths studied, the chemical activation of N 2 must occur via another pathway. Any chemical activation of N 2 at wavelengths > 120 nm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH 4 photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for how we view prebiotic chemistry on early Earth and similar planets.

show abstract

Section: Figmentioning

confidence: 94%

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

et al. 2012

View full text Add to dashboard Cite

show abstract

“…It is clear that the expressions given above for k 2nd and k RA [Eqs. (15) and (17)] lead to Equation (18). Hence, if k 3rd is experimentally…”

Section: Angewandte Chemiementioning

confidence: 98%

“…Examples of such reactions that have been studied in CRESU experiments include those of CH radicals with H 2 , [16] N 2 , [17] and CO, [17] and those of OH radicals with NO, [24] and NO 2 [25] For most of these association reactions, the pressure dependence of the second-order rate constant has been studied in CRESU experiments and five nozzles were constructed to yield a temperature of 53 AE 1 K with densities of the carrier gas (Ar) in the gas jet ranging from 5. 15 [Eq.…”

Section: Rate Constants For Neutral-neutral Reactions and Their Tempementioning

confidence: 99%

“…However, in the case of CH( 2 P) formed from the sequential multiphoton dissociation of CHBr 3 , vibrational levels above v = 0 are significantly populated. Independent kinetic measurements of CH( 2 P, v=0) and CH( 2 P, v=1) were made and provided useful information about the relaxation of vibrationally excited CH radicals in collisions with species such as H 2 [16] CO [17] and N 2 , [17] for which both relaxation and association proceed through the initial formation of a strongly bound complex. [18] Because the sample of radicals produced along the core of the flow is moving rapidly, the reaction under investigation must perturb the radical concentration in the time (150 ms-1 ms) that it takes the gas to flow from the exit of the Laval nozzle to the point from which LIF is observed.…”

Section: Measuring Rate Constantsmentioning

confidence: 99%

See 1 more Smart Citation

Reactions at Very Low Temperatures: Gas Kinetics at a New Frontier

2006

Self Cite

View full text Add to dashboard Cite

Advances in experimental techniques, especially the development of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) method, allow many gas-phase molecular processes to be studied at very low temperatures. This Review focuses on the reactions of molecular and atomic radicals with neutral molecules. Rate constants for almost 50 such reactions have been measured at temperatures as low as 13 K by using the CRESU method. The surprising demonstration that so many reactions between electrically neutral species can be extremely rapid at these very low temperatures has excited interest both from theoreticians and from those seeking to understand the chemistry that gives rise to the 135 or so molecules that are present in low-temperature molecular clouds in the interstellar medium. Theoretical treatments of these reactions are based on the idea that a reaction occurs when the long-range potential between the reagent species brings them into close contact. The astrochemical context, theoretical studies, and the determination of the rate constants of these low-temperature reactions are critically discussed.

show abstract

“…The reaction rates for 12 CH and 12 CD with normal isotopic abundance CO and 13 CO have been studied at 293 K for pressures between 12.5 and 500 Torr and at 100 Torr for temperatures between 293 and 650 K. The pressure and temperature dependence of the addition reaction of CH with CO have been measured. The addition rate coefficient can be fit to the expression 7.2Ϯ0.3ϫ10 Ϫ12 (T/293) Ϫ2.4Ϯ0.2 cm 3 molecule Ϫ1 s Ϫ1 at 100 Torr total pressure ͑He buffer͒.…”

mentioning

confidence: 99%

Association and isotopic exchange reactions of CH(CD)[X 2Π]+CO

Taatjes

1997

The Journal of Chemical Physics

View full text Add to dashboard Cite

Potential energy surface for the CH 3 + HBr → CH 4 + Br hydrogen abstraction reaction: Thermal and stateselected rate constants, and kinetic isotope effectsThe high-pressure range of the reaction CH( 2 Π)+CO+MHCCO+M The reaction rates for 12 CH and 12 CD with normal isotopic abundance CO and 13 CO have been studied at 293 K for pressures between 12.5 and 500 Torr and at 100 Torr for temperatures between 293 and 650 K. The pressure and temperature dependence of the addition reaction of CH with CO have been measured. The addition rate coefficient can be fit to the expression 7.2Ϯ0.3ϫ10 Ϫ12 (T/293) Ϫ2.4Ϯ0.2 cm 3 molecule Ϫ1 s Ϫ1 at 100 Torr total pressure ͑He buffer͒. A fit of the pressure dependence to a Troe expression with F c ϭ0.6 yields a low-pressure rate constant (k 0 ) of 2.4Ϯ0.3ϫ10 Ϫ30 cm 6 molecule Ϫ2 s Ϫ1 . The rate for carbon atom exchange has been measured by comparison of the 13 C labeled and unlabeled reaction rates. The isotopic exchange reaction is 1.0Ϯ0.2ϫ10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 at 20 Torr. The deuterium isotope effect on the exchange rate is large, with an inverse kinetic isotope effect ͑k H /k D ͒ϭ0.28Ϯ0.08 at 20 Torr. This inverse isotope effect reflects the competition between collisional stabilization and isomerization, and is a convolution of isotope effects for the isomerization, unimolecular dissociation, and stabilization rates. The experimental results are consistent with a mechanism for exchange that involves isomerization of an HCCO adduct via an oxiryl intermediate, and indicate that insertion into the C-O bond is not important in this reaction.

show abstract

Pressure and temperature dependence of the rate constants for the association reactions of CH radicals with CO and N2 between 202 and 584 K

Cited by 29 publications

References 30 publications

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Reactions at Very Low Temperatures: Gas Kinetics at a New Frontier

Association and isotopic exchange reactions of CH(CD)[X 2Π]+CO

Contact Info

Product

Resources

About

Pressure and temperature dependence of the rate constants for the association reactions of CH radicals with CO and N2 between 202 and 584 K

Cited by 29 publications

References 30 publications

Nitrogen Incorporation in CH4-N2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH4-N2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Reactions at Very Low Temperatures: Gas Kinetics at a New Frontier

Association and isotopic exchange reactions of CH(CD)[X 2Π]+CO

Contact Info

Product

Resources

About

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation

Nitrogen Incorporation in CH₄-N₂ Photochemical Aerosol Produced by Far Ultraviolet Irradiation