How Many Water Molecules Does it Take to Dissociate HCl?

Vargas-Caamal, Alba; Cabellos, José Luis; Ortíz‐Chi, Filiberto; Rzepa, Henry; Restrepo, Albeiro; Merino, Gabriel

doi:10.1002/chem.201504016

Cited by 48 publications

(63 citation statements)

References 71 publications

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“…Previous studies have revealed that the thermodynamic properties and the stability order of isomers may change at different temperatures. 65,71,84 Thus, understanding the temperature dependence of cluster formation is important, especially at atmospheric temperature. However, because the wall loss of the clusters increases as the temperature decreases, it is hard to perform the relevant experiments at low temperature.…”

Section: Temperature Dependence Of Cluster Formationmentioning

confidence: 99%

Interaction of oxalic acid with dimethylamine and its atmospheric implications

et al. 2017

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Section: Temperature Dependence Of Cluster Formationmentioning

confidence: 99%

Interaction of oxalic acid with dimethylamine and its atmospheric implications

et al. 2017

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“…Aggregation simulations of SIP + H 2 O with the water molecule in random orientations and positions around the center of the SIP cluster.Table S4. Aggregation simulations of the cyclic (H 2 O) 4 cluster with an HCl molecule using three different classes of initial conditions, using different cluster-molecule distances ( d ), relative velocities ( v ), and harmonic constants ( k ), as specified.References ( 53 , 54 )…”

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confidence: 99%

Acid solvation versus dissociation at “stardust conditions”: Reaction sequence matters

et al. 2019

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Chemical reactions at ultralow temperatures are of fundamental importance to primordial molecular evolution as it occurs on icy mantles of dust nanoparticles or on ultracold water clusters in dense interstellar clouds. As we show, studying reactions in a stepwise manner in ultracold helium nanodroplets by mass-selective infrared (IR) spectroscopy provides an avenue to mimic these “stardust conditions” in the laboratory. In our joint experimental/theoretical study, in which we successively add H2O molecules to HCl, we disclose a unique IR fingerprint at 1337 cm−1 that heralds hydronium (H3O+) formation and, thus, acid dissociation generating solvated protons. In stark contrast, no reaction is observed when reversing the sequence by allowing HCl to interact with preformed small embryonic ice-like clusters. Our ab initio simulations demonstrate that not only reaction stoichiometry but also the reaction sequence needs to be explicitly considered to rationalize ultracold chemistry.

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“…In stark contrast to all this previous research, we focus here on the temperature sensitivity of this reaction, having in mind acid‐catalyzed processes at the typical environmental and physiological conditions of about 300 K. Indeed, there is some evidence in the literature for the stabilization of molecular HCl and recombination of salt ions in small water clusters simply by raising the temperature. However, whereas at room temperature, acid dissociation, excess protons and proton transfer have been extensively investigated in bulk water, the same cannot be said when it comes to limiting the amount of water to only a few molecules.…”

Section: Figurementioning

confidence: 99%

Generating Excess Protons in Microsolvated Acid Clusters under Ambient Conditions: An Issue of Configurational Entropy versus Internal Energy

Tudela

Marx

2020

Chemistry A European J

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Acid dissociation, and thus liberation of excess protons in small water droplets, impacts on diverse fields such as interstellar, atmospheric or environmental chemistry. At cryogenic temperatures below 1 K, it is now well established that as few as four water molecules suffice to dissociate the generic strong acid HCl, yet temperature‐driven recombination sets in simply upon heating that cluster. Here, the fundamental question is posed of how many more water molecules are required to stabilize a hydrated excess proton at room temperature. Ab initio path integral simulations disclose that not five, but six water molecules are needed at 300 K to allow for HCl dissociation independently from nuclear quantum effects. In order to provide the molecular underpinnings of these observations, the classical and quantum free energy profiles were decomposed along the dissociation coordinate in terms of the corresponding internal energy and entropy profiles. What decides in the end about acid dissociation, and thus ion pair formation, in a specific microsolvated water cluster at room temperature is found to be a fierce competition between classical configurational entropy and internal energy, where the former stabilizes the undissociated state whereas the latter favors dissociation. It is expected that these are generic findings with broad implications on acid–base chemistry depending on temperature in small water assemblies.

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How Many Water Molecules Does it Take to Dissociate HCl?

Cited by 48 publications

References 71 publications

Interaction of oxalic acid with dimethylamine and its atmospheric implications

Interaction of oxalic acid with dimethylamine and its atmospheric implications

Acid solvation versus dissociation at “stardust conditions”: Reaction sequence matters

Generating Excess Protons in Microsolvated Acid Clusters under Ambient Conditions: An Issue of Configurational Entropy versus Internal Energy

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