Generating excess protons in microsolvated acid clusters under ambient conditions
- 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.
Author: | Ricardo Pérez de TudelaORCiDGND, Dominik MarxGND |
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URN: | urn:nbn:de:hbz:294-98878 |
DOI: | https://doi.org/10.1002/chem.202000864 |
Parent Title (English): | Chemistry – A European journal |
Subtitle (English): | an issue of configurational entropy versus internal energy |
Publisher: | Wiley-VCH |
Place of publication: | Hoboken, New Jersey |
Document Type: | Article |
Language: | English |
Date of Publication (online): | 2023/05/16 |
Date of first Publication: | 2020/02/20 |
Publishing Institution: | Ruhr-Universität Bochum, Universitätsbibliothek |
Tag: | ab initio calculations; acid dissociation; entropy; solvation; thermodynamic integration |
Volume: | 26 |
Issue: | 52 |
First Page: | 11955 |
Last Page: | 11959 |
Note: | Dieser Beitrag ist auf Grund des DEAL-Wiley-Vertrages frei zugänglich. |
Institutes/Facilities: | Lehrstuhl für Theoretische Chemie |
Dewey Decimal Classification: | Naturwissenschaften und Mathematik / Chemie, Kristallographie, Mineralogie |
open_access (DINI-Set): | open_access |
faculties: | Fakultät für Chemie und Biochemie |
Licence (English): | Creative Commons - CC BY 4.0 - Attribution 4.0 International |