Computational study of the I2O5+ H2O = 2 HOIO2 gas-phase reaction

Khanniche, Sarah; Louis, Florent; Cantrel, Laurent; Černušák, Ivan

doi:10.1016/j.cplett.2016.09.023

Cited by 22 publications

(35 citation statements)

References 41 publications

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“…b Calculated from published values of ab initio formation or reaction enthalpies. Normal typescript: CCSD(T)//MP2/aug-cc-pVTZ (AREP) from Galvez et al 32 ; italics: CCSD(T)//B3LYP/aug-cc-pVTZ + AE from Kaltsoyannis and Plane 60 ; underlined: CCSD(T)//M06-2X/aug-cc-pVTZ+LANL2DZ from Kumar et al 30 (concerted pathways); bold: CCSD(T)/CBS//MP2/aug-cc-pVTZ (ECP28) from Khanniche et al 33 .…”

Section: Resultsmentioning

confidence: 99%

“…A reaction of any of these H 2 O…IO x adducts with O 3 to form oxyacids requires substantial bond rearrangement and barriers are expected. Recent ab initio studies have found a substantial barrier in the potential energy surface (PES) of the I 2 O 5 + H 2 O ↔ 2HOIO 2 reaction 30,33 , precluding not only formation of HOIO 2 but also a nucleation mechanism depending on the formation of I 2 O 5 from the HOIO 2 self-reaction 23,30 .…”

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confidence: 99%

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A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides

et al. 2020

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Emitted from the oceans, iodine-bearing molecules are ubiquitous in the atmosphere and a source of new atmospheric aerosol particles of potentially global significance. However, its inclusion in atmospheric models is hindered by a lack of understanding of the first steps of the photochemical gas-to-particle conversion mechanism. Our laboratory results show that under a high humidity and low HOx regime, the recently proposed nucleating molecule (iodic acid, HOIO2) does not form rapidly enough, and gas-to-particle conversion proceeds by clustering of iodine oxides (IxOy), albeit at slower rates than under dryer conditions. Moreover, we show experimentally that gas-phase HOIO2 is not necessary for the formation of HOIO2-containing particles. These insights help to explain new particle formation in the relatively dry polar regions and, more generally, provide for the first time a thermochemically feasible molecular mechanism from ocean iodine emissions to atmospheric particles that is currently missing in model calculations of aerosol radiative forcing.

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Section: Resultsmentioning

confidence: 99%

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A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides

et al. 2020

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“…A new set of thermodynamic data [Δ f H 298 K ° , S 298 K ° , and C p ( T )] was provided. The mechanism of the I 2 O 5 + H 2 O = 2 HOIO 2 gas-phase reaction has also been investigated and elucidated in our group . At atmospheric conditions, the gas-phase reaction of hydration of I 2 O 5 to HOIO 2 was found to be too slow with respect to the nucleation process, whereas for severe accidents, a large excess of iodic acid should be present …”

Section: Introductionmentioning

confidence: 99%

“…Little is known about the gas-phase properties of iodic acid. Few theoretical studies of HOIO 2 are available in the literature, − and experimental evidence of iodine oxide particle formation through the addition of iodic acid has just been published. HIO 3 vapor was observed at Mace Head (Ireland) with concentrations greater than 10 8 molecules cm –3 .…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Reaction Mechanism and Kinetics of Iodic Acid with OH Radical Using Quantum Chemistry

Khanniche

Louis

Cantrel

et al. 2017

ACS Earth Space Chem.

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In this paper, the mechanism of the HOIO 2 + OH → products reaction is investigated using quantum chemistry tools. Two pathways are considered: HOIO 2 + OH → OIO 2 + H 2 O and HOIO 2 + OH → OIO + H 2 O 2 . The potential energy surfaces are calculated at the CCSD(T)/ CBS(D,T)//B3LYP/aug-cc-pVTZ level of theory. The OH radical was found to attack iodic acid from either the frontside (TS Habs ) or the topside (TS OHabs ), subsequently leading to Hor OH-transfer channels. Reaction enthalpies and standard Gibbs free reaction energies at 298 K are provided. The values indicate that only the HOIO 2 + OH → OIO 2 + H 2 O channel is exothermic and exergonic. Theoretical prediction of the kinetic parameters is performed within the framework of the transition state theory (TST) and variational transition state theory (VTST). The rate constants (in cm 3 molecule −1 s −1 ) for temperatures from 250 to 2500 K are k Habs (T) = 1.76 × 10 −22 T 2.39 exp(−3.5 (kJ mol −1 )/RT) and k OHabs (T) = 3.16 × 10 −21 T 2.57 exp(−96.2 (kJ mol −1 )/RT). The HOIO 2 + OH overall reaction is significantly dominated by the HOIO 2 + OH → OIO 2 + H 2 O channel for tropospheric temperatures. The main outcomes of this work are as follows: (i) The lifetime of iodic acid toward its removal by OH radicals is extremely long (1336 years), enabling its transportation to different locations around the Earth (marine, polar, and continental), as confirmed by recent field measurements; other possible loss pathways under clear sky (gas phase) and cloudy (aqueous phase) conditions could reduce its atmospheric lifetime. (ii) The thermochemical properties of the OIO 2 radical are provided: Δ f H 298 K

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“…Hence, these observations suggest that I 2 O 5 reacts with water to generate HIO 3 . The reaction between I 2 O 5 and H 2 O is precluded by a large barrier in the PES, 30 but recent ab initio calculations at the CCSD(T)//M06-2X/aug-ccpVTZ-PP + ECP28 level 32 indicate that hydrolysis of I 2 O 5 by the water dimer is feasible …”

Section: Discussionmentioning

confidence: 99%

Insights into the Chemistry of Iodine New Particle Formation: The Role of Iodine Oxides and the Source of Iodic Acid

et al. 2022

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Iodine chemistry is an important driver of new particle formation in the marine and polar boundary layers. There are, however, conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that the photooxidation of iodine produces iodine oxides (I x O y ), which are well-known particle precursors. By contrast, nitrate anion chemical ionization mass spectrometry (CIMS) observations in field and environmental chamber studies have been interpreted as evidence of a dominant role of iodic acid (HIO 3 ) in iodine-driven particle formation. Here, we report flow tube laboratory experiments that solve these discrepancies by showing that both I x O y and HIO 3 are involved in atmospheric new particle formation. I 2 O y molecules ( y = 2, 3, and 4) react with nitrate core ions to generate mass spectra similar to those obtained by CIMS, including the iodate anion. Iodine pentoxide (I 2 O 5 ) produced by photolysis of higher-order I x O y is hydrolyzed, likely by the water dimer, to yield HIO 3 , which also contributes to the iodate anion signal. We estimate that ∼50% of the iodate anion signals observed by nitrate CIMS under atmospheric water vapor concentrations originate from I 2 O y . Under such conditions, iodine-containing clusters and particles are formed by aggregation of I 2 O y and HIO 3 , while under dry laboratory conditions, particle formation is driven exclusively by I 2 O y . An updated mechanism for iodine gas-to-particle conversion is provided. Furthermore, we propose that a key iodine reservoir species such as iodine nitrate, which we observe as a product of the reaction between iodine oxides and the nitrate anion, can also be detected by CIMS in the atmosphere.

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Computational study of the I2O5+ H2O = 2 HOIO2 gas-phase reaction

Cited by 22 publications

References 41 publications

A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides

A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides

Investigation of the Reaction Mechanism and Kinetics of Iodic Acid with OH Radical Using Quantum Chemistry

Insights into the Chemistry of Iodine New Particle Formation: The Role of Iodine Oxides and the Source of Iodic Acid

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