Observation of a large negative temperature dependence for rate coefficients of reactions of OH with oxygenated volatile organic compounds studied at 86–112 K

Shannon, Robin J.; Taylor, Sally; Goddard, A.; Blitz, Mark A.; Heard, Dwayne E.

doi:10.1039/c0cp00918k

Cited by 53 publications

(83 citation statements)

References 16 publications

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“…These results further highlight the role that a pre-reaction hydrogen bonded OH complex plays in low temperature kinetics, in this case the adduct is sufficiently long lived to facilitate tunnelling, the majority proceeding via the higher activation barrier to form CH 3 O. In previous studies, for example of the reaction between OH with acetone, we had also observed a dramatic increase in the rate coefficient at very low temperatures [28], although a significant pressure dependence of the rate coefficient suggested collisional stabilisation of the complex without tunnelling to products [26].…”

Section: Discussionmentioning

confidence: 68%

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

et al. 2013

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Understanding the abundances of molecules observed in dense interstellar clouds requires knowledge of the rates of gas phase reactions between two neutral species. However, reactions possessing an activation barrier were considered too slow to play any important role at the low temperatures in these clouds. Here we show that despite the presence of a barrier the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol, one of the most abundant organic molecules in space, is almost two orders of magnitude larger at 63K than previously measured at ~200K. We also observe formation of the methoxy radical product that was recently detected in space. These results are interpreted through the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum mechanical tunnelling to form products. We postulate that this tunnelling

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Section: Discussionmentioning

confidence: 68%

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

et al. 2013

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“…14,17,22 Furthermore, the formation of the longer-lived complex at low temperature enhances the probability of hydrogen atom transfer via quantum mechanical tunneling to form products. It is postulated that this mechanism may be general for reactions of OH with oxygenated volatile compounds, and that these reactions should be considered in networks describing the chemistry of the interstellar medium.…”

Section: Discussionmentioning

confidence: 99%

“…However, recent low temperature studies of neutral-neutral reactions have shown that the temperature dependence of their rate coefficients is often complex and poorly understood, and so kinetic data close to ambient temperatures cannot simply be extrapolated. [14][15][16][17] From previous studies it is acknowledged that at temperatures above 200 K, the reactions of OH with alcohols appear to proceed via a direct, bimolecular hydrogen abstraction mechanism (R1). 2,6,17,18 + R1…”

Section: Introductionmentioning

confidence: 99%

Measurements of Rate Coefficients for Reactions of OH with Ethanol and Propan-2-ol at Very Low Temperatures

et al. 2014

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The low temperature kinetics of the reactions of OH with ethanol and propan-2-ol have been studied using a pulsed Laval nozzle apparatus coupled with pulsed laser photolysis -laser induced fluorescence (PLP-LIF) spectroscopy. The rate coefficients for both reactions have been found to increase significantly as the temperature is lowered, by~a factor of 18 between 293 and 54 K for ethanol, and by~10 between 298 and 88 K for OH + propan-2-ol. The pressure dependence of the rate coefficients provide evidence for two reaction channels; a zero pressure bimolecular abstraction channel leading to products and collisional stabilization of a weakly bound OH-alcohol complex. The presence of the abstraction channel at low temperatures is rationalized by a quantum mechanical tunneling mechanism, most likely through the barrier to hydrogen abstraction from the OH moiety on the alcohol.

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“…The experimental setup of the pulsed Laval nozzle apparatus utilised in this study has been discussed in detail previously so only a brief description is given here [12][13][21][22] . Methanol was degassed and its vapour pressure was admitted to an evacuated cylinder where it was diluted with N 2 (Ar) and allowed to mix overnight before use.…”

Section: Plp-lif-laval Nozzlementioning

confidence: 99%

Low Temperature Kinetics of the CH₃OH + OH Reaction

et al. 2014

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The rate constant of the reaction between methanol and the hydroxyl radical has been studied in the temperature range 56-202 K by pulsed laser photolysis-laser induced fluorescence in two separate experiments using either a low temperature flow tube coupled to a time of flight mass spectrometer or a pulsed Laval nozzle apparatus. The two independent techniques yield rate constants which are in mutual agreement and consistent with the results reported previously below 82 K [Shannon et al., Nature Chemistry, 2013, 5, 745-749] and above 210 K [Dillon et al., Phys. Chem. Chem. 2005, 7, 349-355], showing a very sharp increase with decreasing temperature with an onset around 180 K. This onset is also signalled by strong chemiluminescence tentatively assigned to formaldehyde, which is consistent with the formation of the methoxy radical at low temperature by quantum tunnelling, and its subsequent reaction with H and OH. Our results add confidence to the previous low temperature rate constant measurements and consolidate the experimental reference dataset for further theoretical work required to describe quantitatively the tunnelling mechanism operating in this reaction. An additional measurement of the rate constant at 56 K yielded a value of (4.9 ± 0.8) × 10 −11 cm 3 molecule −1 s −1 (2σ), showing that the rate constant is increasing less rapidly at temperatures below 70 K.

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Observation of a large negative temperature dependence for rate coefficients of reactions of OH with oxygenated volatile organic compounds studied at 86–112 K

Cited by 53 publications

References 16 publications

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

Measurements of Rate Coefficients for Reactions of OH with Ethanol and Propan-2-ol at Very Low Temperatures

Low Temperature Kinetics of the CH₃OH + OH Reaction

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Observation of a large negative temperature dependence for rate coefficients of reactions of OH with oxygenated volatile organic compounds studied at 86–112 K

Cited by 53 publications

References 16 publications

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling

Measurements of Rate Coefficients for Reactions of OH with Ethanol and Propan-2-ol at Very Low Temperatures

Low Temperature Kinetics of the CH3OH + OH Reaction

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Low Temperature Kinetics of the CH₃OH + OH Reaction