Effect of composition and pressure on gas-phase reaction rate coefficients

Abstract. Pulsed laser excitation of NO2 (532–647 nm) or NO3 (623–662 nm) in the presence of H2O was used to initiate the gas-phase reaction NO2∗+H2O → products (Reaction R5) and NO3∗+H2O → products (Reaction R12). No evidence for OH production in Reactions (R5) or (R12) was observed and upper limits for OH production of k5b/k5<1×10-5 and k12b/k12<0.03 were assigned. The upper limit for k5b∕k5 renders this reaction insignificant as a source of OH in the atmosphere and extends the studies (Crowley and Carl, 1997; Carr et al., 2009; Amedro et al., 2011) which demonstrate that the previously reported large OH yield by Li et al. (2008) was erroneous. The upper limit obtained for k12b∕k12 indicates that non-reactive energy transfer is the dominant mechanism for Reaction (R12), though generation of small but significant amounts of atmospheric HOx and HONO cannot be ruled out. In the course of this work, rate coefficients for overall removal of NO3∗ by N2 (Reaction R10) and by H2O (Reaction R12) were determined: k10=(2.1±0.1)×10-11 cm3 molecule−1 s−1 and k12=(1.6±0.3)×10-10 cm3 molecule−1 s−1. Our value of k12 is more than a factor of 4 smaller than the single previously reported value.

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Rate coefficients for the gas-phase reaction of OH radicals with selected dihydroxybenzenes and benzoquinones

International Journal of Chemical Kinetics ◽

10.1002/1097-4601(2000)32:11<696::aid-kin5>3.0.co;2-n ◽

2000 ◽

Vol 32 (11) ◽

pp. 696-702 ◽

Cited By ~ 30

Author(s):

R. I. Olariu ◽

I. Barnes ◽

K. H. Becker ◽

B. Klotz

Keyword(s):

Gas Phase ◽

Rate Coefficients ◽

Oh Radicals ◽

Phase Reaction ◽

Gas Phase Reaction

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Low temperature gas phase reaction rate coefficient measurements: Toward modeling of stellar winds and the interstellar medium

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007531 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 382-383

Author(s):

Niclas A. West ◽

Edward Rutter ◽

Mark A. Blitz ◽

Leen Decin ◽

Dwayne E. Heard

Keyword(s):

Low Temperature ◽

Interstellar Medium ◽

Gas Phase ◽

Low Temperatures ◽

Reaction Rate ◽

Rate Coefficient ◽

Building Blocks ◽

Rate Coefficients ◽

Stellar Winds ◽

Phase Reaction

AbstractStellar winds of Asymptotic Giant Branch (AGB) stars are responsible for the production of ∼85% of the gas molecules in the interstellar medium (ISM), and yet very few of the gas phase rate coefficients under the relevant conditions (10 – 3000 K) needed to model the rate of production and loss of these molecules in stellar winds have been experimentally measured. If measured at all, the value of the rate coefficient has often only been obtained at room temperature, with extrapolation to lower and higher temperatures using the Arrhenius equation. However, non-Arrhenius behavior has been observed often in the few measured rate coefficients at low temperatures. In previous reactions studied, theoretical simulations of the formation of long-lived pre-reaction complexes and quantum mechanical tunneling through the barrier to reaction have been utilized to fit these non-Arrhenius behaviours of rate coefficients.Reaction rate coefficients that were predicted to produce the largest change in the production/loss of Complex Organic Molecules (COMs) in stellar winds at low temperatures were selected from a sensitivity analysis. Here we present measurements of rate coefficients using a pulsed Laval nozzle apparatus with the Pump Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique. Gas flow temperatures between 30 – 134 K have been produced by the University of Leeds apparatus through the controlled expansion of N2 or Ar gas through Laval nozzles of a range of Mach numbers between 2.49 and 4.25.Reactions of interest include those of OH, CN, and CH with volatile organic species, in particular formaldehyde, a molecule which has been detected in the ISM. Kinetics measurements of these reactions at low temperatures will be presented using the decay of the radical reagent. Since formaldehyde and the formal radical (HCO) are potential building blocks of COMs in the interstellar medium, low temperature reaction rate coefficients for their production and loss can help to predict the formation pathways of COMs observed in the interstellar medium.

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