Kinetics and mechanism of hydroperoxo and hydroperoxo-d disproportionations

Kircher, C. C.; Sander, Stanley P.

doi:10.1021/j150654a029

Cited by 139 publications

(196 citation statements)

References 8 publications

(12 reference statements)

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“…Negative temperature dependence is often observed for reactions involving water clusters. [78][79][80] This effect is due to the decreasing formation probability of clusters in the gas phase with increasing temperature. The calculations here do not include such an effect, since the model deals with clusters formed on a water surface.…”

Section: Resultsmentioning

confidence: 99%

Catalytic Role for Water in the Atmospheric Production of ClNO

et al. 2010

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High level ab initio calculations of clusters comprised of water, HCl, and ON-ONO2 are used to study nitrosyl chloride (ClNO) formation in gas phase water clusters, which are also mimics for thin water films present at environmental interfaces. Two pathways are considered, direct formation from the reaction of gaseous HCl with ON-ONO2 and an indirect pathway involving the hydrolysis of ON-ONO2 to form HONO, followed by the reaction of HONO with HCl to form ClNO. Surprisingly, direct formation of ClNO is found to be the dominant channel in the presence of water despite the possibility of a competing hydrolysis of ON-ONO2 to form HONO. A single water molecule effectively catalyzes the ON-ONO2 + HCl reaction, and in the presence of two or more water molecules the reaction to form ClNO becomes spontaneous. Direct formation of ClNO is fast at room and ice temperatures, indicating the possible significance of this pathway for chlorine activation chemistry in both the polar and midlatitude troposphere, in volcanic plumes and indoors. The reaction enthalpies, activation energies, and rate constants for all studied reactions are reported. The results are discussed in light of recent experiments. Disciplines Chemistry CommentsReprinted (adapted) Jerusalem, 91904, Israel ReceiVed: December 24, 2009; ReVised Manuscript ReceiVed: February 21, 2010 High level ab initio calculations of clusters comprised of water, HCl, and ON-ONO 2 are used to study nitrosyl chloride (ClNO) formation in gas phase water clusters, which are also mimics for thin water films present at environmental interfaces. Two pathways are considered, direct formation from the reaction of gaseous HCl with ON-ONO 2 and an indirect pathway involving the hydrolysis of ON-ONO 2 to form HONO, followed by the reaction of HONO with HCl to form ClNO. Surprisingly, direct formation of ClNO is found to be the dominant channel in the presence of water despite the possibility of a competing hydrolysis of ON-ONO 2 to form HONO. A single water molecule effectively catalyzes the ON-ONO 2 + HCl reaction, and in the presence of two or more water molecules the reaction to form ClNO becomes spontaneous. Direct formation of ClNO is fast at room and ice temperatures, indicating the possible significance of this pathway for chlorine activation chemistry in both the polar and midlatitude troposphere, in volcanic plumes and indoors. The reaction enthalpies, activation energies, and rate constants for all studied reactions are reported. The results are discussed in light of recent experiments.

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Section: Resultsmentioning

confidence: 99%

Catalytic Role for Water in the Atmospheric Production of ClNO

et al. 2010

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“…The function of this chemistry might be to form reactive intermediates next to the antigen that would react with it to nick the protein recognized by the Ab, making it more susceptible to attack by other enzymes in the macrophage. Alternatively, the function of the Ab might be as a 1 (32) and in the pulse radiolysis of air-saturated perchloric acid solution (25) (37)(38)(39)(40)(41)(42). This reaction possesses a negative activation barrier (40)(41)(42), but no molecular level mechenistic study has been reported.…”

Section: Summary Of the H2o3 Plus 1 O2 Mechanism (Pathway Ii)mentioning

confidence: 99%

The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

Muller

Goddard

2002

Proc. Natl. Acad. Sci. U.S.A.

105

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Abs efficiently catalyze the conversion of molecular singlet oxygen ( 1 O2) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) to delineate the most plausible mechanisms for the observed efficient conversion of water to HOOH. We find two reasonable pathways. In Pathway I, (i) H2O catalyzes the reaction of 1 O2 with a second water to form HOOOH; (ii) two HOOOH form a dimer, which rearranges to form the HOO-HOOO ؉ H2O complex; (iii) HOO-HOOO rearranges to HOOH-OOO, which subsequently reacts with H2O to form H2O4 ؉ HOOH; and (iv) H2O4 rearranges to the cyclic dimer (HO2)2, which in turn forms HOOH plus 1 O2 or 3 O2. Pathway II differs in that step ii is replaced with the reaction between HOOOH and 1 O2, leading to the formation of HOO-HOOO. This then proceeds to similar products. For a system with 18 The results lead to plausible mechanisms in good agreement with the Scripps isotope experiments. The Discussion talks about these results, suggesting that these mechanisms account for the Scripps Ab results and they may also be significant for understanding related processes in biochemistry, combustion, explosions, atmospheric chemistry, and radiation chemistry of aqueous systems. Computational DetailsAll QM calculations use the Becke three-parameter hybrid functional with Lee-Yang-Parr correlation functional (B3LYP) flavor of density functional theory (3-7), which includes a generalized gradient approximation and some exact exchange. The 6-31G** basis set (8, 9) was used on all atoms for a full geometry optimization. Vibrational frequencies (from the analytic Hessian) were calculated to ensure that each minimum is a true local minimum (containing only positive frequencies) and that each transition state has only a single imaginary frequency (negative eigenvalue of the Hessian). All QM calculations were carried out with JAGUAR (10-12). Some of these energetics were included in ref. 2.To obtain more accurate energetics, we carried out calculations with the cc-pVTZ basis set (13) by using the optimized geometries from the 6-31G** basis. Such QM calculations lead to an accuracy of around 3 kcal͞mol for simple organic molecules (14).For molecules such as 1 O 2 and O 3 , which have significant open shell character, standard density functional theory methods often lead to much larger errors. Thus, with B3LYP, the singlet and triplet gap for O 2 is ⌬E ( 1 ⌬ g Ϫ 3 ⌺ g Ϫ ) ϭ 10.4 kcal͞mol, in poor agreement with the experimental value of 22.5 kcal͞mol (15). Consequently, we used spin projection techniques (16) to ensure a proper description of the complexes involving 1 O 2 . This leads to ⌬E ( 1 ⌬ g Ϫ 3 ⌺ g Ϫ ) ϭ 20.5 kcal͞mol, in good agreement with experiment.The calculated vibrational frequencies (with no empirical scaling) were used to calculate the zero point energy and temperature corrections so that all energetics are reported for ⌬H (298K), in kcal͞mol. QM Calculations and Plausible MechanismsFormation of H2O2 from the Reaction Between Two H2O3. First, we examined...

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“…This reaction exhibits a number of interesting features that have significance for determining the rate constant under atmospheric conditions [1]. These include a pronounced negative activation energy of -1.2 kcal mol-1 [2][3][4][5], a definite pressure dependence [6,7], and an enhancement of the rate constant by small amounts of water vapor [8,9]. The addition of small amounts of NHs initially enhances but then suppresses the reaction [9,10].…”

Section: Introductionmentioning

confidence: 99%

“…The addition of small amounts of NHs initially enhances but then suppresses the reaction [9,10]. The self-reaction of D0 2 shows similar behavior but with a smaller rate constant [9] and a weaker pressure dependence [2].…”

Section: Introductionmentioning

confidence: 99%

Self‐Reaction of HO₂ and DO₂: Negative temperature dependence and pressure effects

Mozurkewich

Benson

1985

Int J of Chemical Kinetics

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The negative temperature dependence, pressure dependence, and isotope effects of the self-reaction of HO z are modeled~using RRKM theory, by assuming that the reac· tion proceeds via a cyclic, hydrogen-bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO z self-reaction is due to the approach to the high-pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high·pressure limit of the self-reaction of HO z .

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Kinetics and mechanism of hydroperoxo and hydroperoxo-d disproportionations

Cited by 139 publications

References 8 publications

Catalytic Role for Water in the Atmospheric Production of ClNO

Catalytic Role for Water in the Atmospheric Production of ClNO

The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

Self‐Reaction of HO₂ and DO₂: Negative temperature dependence and pressure effects

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Kinetics and mechanism of hydroperoxo and hydroperoxo-d disproportionations

Cited by 139 publications

References 8 publications

Catalytic Role for Water in the Atmospheric Production of ClNO

Catalytic Role for Water in the Atmospheric Production of ClNO

The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

Self‐Reaction of HO2 and DO2: Negative temperature dependence and pressure effects

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Self‐Reaction of HO₂ and DO₂: Negative temperature dependence and pressure effects