Gas-phase kinetics of CH3CHO with OH radicals between 11.7 and 177.5 K.
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ABSTRACT:
SUBMITTER: Blazquez S
PROVIDER: S-EPMC7116299 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The present relative kinetic study reports on the experimentally determined gas-phase reaction rate coefficients of OH radicals with a series of seven cis-3-hexenyl esters. The experiments were carried out in the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi (ESC-Q-UAIC), Romania, at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. In situ long-path Fourier transform infrared (FTIR) spectroscopy was used to monitor cis-3-hexenyl formate (Z3HF, (Z)-CH3CH2CH═CH(CH2)2OC(O)H), cis-3-hexenyl acetate (Z3HAc, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH3), cis-3-hexenyl isobutyrate (Z3HiB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH(CH3)2), cis-3-hexenyl 3-methylbutanoate (Z3H3MeB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH(CH3)2), cis-3-hexenyl hexanoate (Z3HH, (Z)-CH3CH2CH═CH(CH2)2OC(O)(CH2)4CH3), cis-3-hexenyl cis-3-hexenoate (Z3HZ3H, (Z,Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH═CHCH2CH3), cis-3-hexenyl benzoate (Z3HBz, (Z)-CH3CH2CH═CH(CH2)2OC(O)C6H5), and the reference compounds. The following reaction rate coefficients (in 10-11 cm3 molecule-1 s-1) were obtained for the OH radical-initiated gas-phase oxidation of cis-3-hexenyl esters: (4.13 ± 0.45) for Z3HF, (4.19 ± 0.38) for Z3HAc, (4.84 ± 0.39) for Z3HiB, (5.39 ± 0.61) for Z3H3MeB, (7.00 ± 0.56) for Z3HH, (10.58 ± 1.40) for Z3HZ3H, and (3.41 ± 0.28) for Z3HBz. The results are discussed in terms of hexenyl ester reactivity and compared with the available literature data and structure-activity relationship (SAR) estimates. The atmospheric implications based on the average lifetimes of the investigated cis-3-hexenyl esters are discussed in the present study. The gas-phase rate coefficients for OH radical reactions are given herein for the first time for cis-3-hexenyl isobutyrate, cis-3-hexenyl 3-methylbutanoate, cis-3-hexenyl hexanoate cis-3-hexenyl cis-3-hexenoate, and cis-3-hexenyl benzoate. The newly determined gas-phase reaction rate coefficients provide new information for existing kinetic databases and contribute to the further development of SAR methodologies useful for predicting the reactivity of oxygenated volatile organic compounds.
| S-EPMC11299184 | biostudies-literature
Project description:The reactivity of methanol (CH3OH) toward the hydroxyl (OH) radical was investigated in the temperature range 11.7-177.5 K using the CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) technique. In the present study, the temperature dependence of the rate coefficient for the OH + CH3OH reaction, k(T), has been revisited and additional experimental and computational data are reported. New kinetic measurements were performed to fill the existing gaps (<22 K, 22-42 K and 88-123 K), reporting k(T < 20 K) for the first time. The lowest temperature ever achieved by a pulsed CRESU has been obtained in this work (11.7 K). k(T) abruptly increases by almost 2 orders of magnitude from 177.5 K to around 100 K. At T < 100 K, this increase is less pronounced, reaching the capture limit at temperatures below 22 K. The pressure dependence of k(T) has been investigated for selected temperatures and gas densities (1.5 × 1016 to 4.3 × 1017 cm-3), combining our results with those previously reported. No dependence was observed within the experimental uncertainties below 110 K. The high- and low-pressure rate coefficients, kHPL(T) and kLPL(T), were also studied in detail using high-level quantum chemical and theoretical kinetic methodologies, closely reproducing the experimental data between 20 and 400 K. The results suggest that the experimental data are near the high pressure limit at the lowest temperatures, but that the reaction remains a fast and effective source of CH2OH and CH3O at the low pressures and temperatures prevalent in the interstellar medium.
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Project description:The potential energy surface (PES) of the C6H5 + NH2 reaction has been investigated by using ab initio CCSD(T)//B3LYP/6-311++G(3df,2p) calculations. The conventional transition-state theory (TST) and the variable reaction coordinate-TST (VRC-TST) have been used to predict the rate constants for the channels possessing tight and barrierless transition states, respectively. The Rice-Ramsperger-Kassel-Marcus/Master equation (RRKM/ME) theory has been utilized to determine the pressure-dependent rate constants for these reactions. The PES shows that the reaction begins with an exothermic barrierless addition of NH2 to C6H5 producing the vital intermediate state, namely, aniline (C6H5NH2, IS1). Once IS1 is generated, it can further isomerize to various intermediate states, which can give rise to different products, including PR4 (4,5,6-trihydro-1-amino phenyl + H2), PR5 (3,4,5,6-tetrahydro phenyl + NH3), PR6 (2,3,5,6-tetrahydro-1-imidogen phenyl + H2), PR9 (3,4,5,6-tetrahydro-1-imidogen phenyl + H2), and PR10 (2,5,6-trihydro-1-amino phenyl + H2), of which the most stable product, PR5, was formed by the most favorable channel going through the two advantageous transition states T1/11 (-28.9 kcal/mol) and T11P5 (-21.5 kcal/mol). The calculated rate constants for the low-energy channel, 1.37 × 10-9 and 2.16 × 10-11 cm3 molecule-1 s-1 at T = 300, P = 1 Torr and T = 2000 K, P = 760 Torr, respectively, show that the title reaction is almost pressure- and temperature-dependent. The negative temperature-dependent rate coefficients can be expressed in the modified Arrhenius form of k 1 = 8.54 × 1013 T -7.20 exp (-7.07 kcal·mol-1/RT) and k 2 = 2.42 × 1015 T -7.61 exp (-7.75 kcal·mol-1/RT) at 1 and 10 Torr, respectively, and in the temperature range of 300-2000 K. The forward and reverse rate coefficients as well as the high-pressure equilibrium constants of the C6H5 + NH2 ↔ IS1 process were also predicted; their values revealed that its kinetics do not depend on pressure at low temperature but strongly depend on pressure at high temperature. Moreover, the predicted formation enthalpies of reactants and the enthalpy changes of some channels are in good agreement with the experimental results.
| S-EPMC6977206 | biostudies-literature
Project description:The kinetics of the reaction of hydroxyl radicals with chlorobenzene was studied experimentally using a pulsed laser photolysis/pulsed laser induced fluorescence technique over a wide range of temperatures, 298-670 K, and at pressures between 13.33 and 39.92 kPa. The bimolecular rate constants demonstrate different behavior at low and high temperatures. At room temperature, T = 298.8 +/- 1.5 K, the rate constant is equal to (6.02 +/- 0.34) x 10(-13) cm3 molecule(-1) s(-1); at high temperatures (474-670 K), the rate constant values are significantly lower and have a positive temperature dependence that can be described by an Arrhenius expression k1(T) = (1.01 +/- 0.35) x 10(-11) exp[(-2490 +/- 170 K)/T] cm3 molecule(-1) s(-1). This behavior is consistent with the low-temperature reaction being dominated by reversible addition and the high-temperature reaction representing abstraction and addition-elimination channels. The potential energy surface of the reaction was studied using quantum chemical methods, and a transition state theory model was developed for all reaction channels. The temperature dependences of the high-temperature rate constants obtained in calculations using the method of isodesmic reactions for transition states (IRTS) and the CBS-QB3 method are in very good agreement with experiment, with deviations smaller than the estimated experimental uncertainties. The G3//B3LYP-based calculated rate constants are in disagreement with the experimental values. The IRTS-based model was used to provide modified Arrhenius expressions for the temperature dependences of the rate constant for the abstraction and addition-elimination (Cl replacement) channels of the reaction.
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Project description:Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals and Cl atoms were obtained at atmospheric pressure and 298 K. The experiments were performed in a 480 L borosilicate glass photoreactor in synthetic air coupled to a long path "in situ" FTIR spectrometer. The rate coefficients obtained by averaging the values from different experiments were: k OH = (2.58 ± 0.21) × 10-11 cm3 per molecule per s and k Cl = (2.49 ± 0.19) × 10-10 cm3 per molecule per s. The kinetic values were compared with related alkyl thiols and homologous alkyl alcohols, where it was found that thiols react faster with both oxidants, OH radicals and Cl atoms. SO2 and 2-butanone were the major products identified for the reactions of 2-butanethiol with OH radicals and Cl atoms. The product yield of the reaction of 2-butanethiol and OH radicals were (81 ± 2)%, and (42 ± 1)% for SO2 and 2-butanone, respectively. For the reactions of 2-butanethiol with Cl atom, yields of SO2 and 2-butanone were (59 ± 2)% and (39 ± 2)%, respectively. A degradation mechanism was proposed for the pathways that leads to formation of identified products. The product distribution observed indicated that the H-atom of the S-H group abstraction channel is the main pathway for the reaction of OH radicals and Cl atoms with 2-butanethiol.
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Project description:A detailed computational investigation is executed on the reaction between NO3 and CH[triple bond, length as m-dash]CCH2OH at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. Addition/elimination and H-abstraction mechanisms are found for the NO3 + CH[triple bond, length as m-dash]CCH2OH reaction, and they could compete with each other. The most feasible addition/elimination pathway through a series of central-C addition, 1,4-H migration to generate intermediates IM1 (CHCONO2CH2OH) and IM3 (CH2CONO2CH2O), and then IM3 directly decompose into product P2 (CH2CONO2CHO + H). The dominant H-abstraction pathway is abstracting the H atom of the -CH2- group to generate h-P1 (CHCCHOH + HNO3). RRKM-TST theory was used to compute the kinetics and product branching ratios of the NO3 + CH[triple bond, length as m-dash]CCH2OH reaction at 200-3000 K. The rate constants at 298 K are consistent with the experimental values. The lifetime of CH[triple bond, length as m-dash]CCH2OH is estimated to be 59.72 days at 298 K. The implicit solvent model was used to examine the solvent effect on the total reaction. Based on the quantitative structure-activity relationship (QSAR) model, the toxicity during the degradation process is increased towards fish, and decreased towards daphnia and green algae.
| S-EPMC11341969 | biostudies-literature
Project description:The interesting properties of Mobius structure and boron-carbon-nitride (BCN) inspired this research to study different characteristics of Mobius BCN (MBCN) nanoribbon. The structural stability and vibrational, electrical and optical properties are analysed using the density functional theory. The gas-sensing ability of the modelled MBCN structure was also studied for methane, hydrogen sulfide, ammonia, phosgene and methanol gases. The negative adsorption energy and alteration of electronic bandgap verified that MBCN is very sensitive toward the selected gases. The complex structures showed a high absorption coefficient with strong chemical potential and 7 ps-0.3 ms recovery time. The negative change in entropy signifies that all the complex structures were thermodynamically stable. Among the selected gases, the MBCN showed the strongest interaction with methanol gas.
| S-EPMC9627448 | biostudies-literature
Project description:Focused-electron-beam-induced deposition (FEBID) is a powerful nanopatterning technique where electrons trigger the local dissociation of precursor molecules, leaving a deposit of non-volatile dissociation products. The fabrication of high-purity gold deposits via FEBID has significant potential to expand the scope of this method. For this, gold precursors that are stable under ambient conditions but fragment selectively under electron exposure are essential. Here, we investigated the potential gold precursor (CH3)AuP(CH3)3 using FEBID under ultra-high vacuum (UHV) and spectroscopic characterization of the corresponding metal-containing deposits. For a detailed insight into electron-induced fragmentation, the deposit's composition was compared with the fragmentation pathways of this compound through dissociative ionization (DI) under single-collision conditions using quantum chemical calculations to aid the interpretation of these data. Further comparison was made with a previous high-vacuum (HV) FEBID study of this precursor. The average loss of about 2 carbon and 0.8 phosphor per incident was found in DI, which agreed well with the carbon content of the UHV FEBID deposits. However, the UHV deposits were found to be as good as free of phosphor, indicating that the trimethyl phosphate is a good leaving group. Differently, the HV FEBID experiments showed significant phosphor content in the deposits.
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Project description:The role of water vapor (H2O) and its hydrogen-bonded complexes in the gas-phase reactivity of organic compounds with hydroxyl (OH) radicals has been the subject of many recent studies. Contradictory effects have been reported at temperatures between 200 and 400 K. For the OH + acetaldehyde reaction, a slight catalytic effect of H2O was previously reported at temperatures between 60 and 118 K. In this work, we used Laval nozzle expansions to reinvestigate the impact of H2O on the OH-reactivity with acetaldehyde between 21.7 and 135.0 K. The results of this comprehensive study demonstrate that water, instead, slows down the reaction by factors of ∼3 (21.7 K) and ∼2 (36.2-89.5 K), and almost no effect of added H2O was observed at 135.0 K.
| S-EPMC7611909 | biostudies-literature
Project description:The rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10-13 cm3 molecule-1 s-1), for OH + CH3OH (+ NH3) [1.9 × 10-21 cm3 molecule-1 s-1] and for OH + CH3OH (+ H2O) [8.1 × 10-16 cm3 molecule-1 s-1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.
| S-EPMC8190139 | biostudies-literature