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Article: Solvation processes in steam: Ab initio calculations of ion-solvent structures and clustering equilibria

TitleSolvation processes in steam: Ab initio calculations of ion-solvent structures and clustering equilibria
Authors
KeywordsAggregate
Aqueous solution
Equilibrium
Ion
Mass spectrometry
Issue Date2008
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/gca
Citation
Geochimica Et Cosmochimica Acta, 2008, v. 72 n. 14, p. 3293-3310 How to Cite?
AbstractReports of the high ion content of steam and low-density supercritical fluids date back to the work of Carlon [Carlon H. R. (1980) Ion content of air humidified by boiling water.J. Appl.Phys.51, 171-173], who invoked ion and neutral-water clustering as mechanism to explain why ions partition into the low-density aqueous phase. Mass spectrometric, vibrational spectroscopic measurements and quantum chemical calculations have refined this concept by proposing strongly bound ion-solvent aggregates and water clusters such as Eigen- and Zundel-type proton clusters H3O+·(H2O)m and the more weakly bound water oligomers (H2O)m. The extent to which these clusters affect fluid chemistry is determined by their abundance, however, little is known regarding the stability of such moieties in natural low-density high-temperature fluids. Here we report results from quantum chemical calculations using chemical-accuracy multi-level G3 (Curtiss-Pople) and CBS-Q theory (Peterson) to address this question. In particular, we have investigated the cluster structures and clustering equilibria for the ions H3 O+ · (H2 O)m (H2 S)n, NH4 + · (H2 O)m (H2 S)n and H3S+·(H2O)m(H2S)n, where m ≤ 6 and n ≤ 4, at 300-1000 K and 1 bar as well as under vapor-liquid equilibrium conditions between 300 and 646 K. We find that incremental hydration enthalpies and entropies derived from van't Hoff analyses for the attachment of H2O and H2S onto H3O+, NH4 + and H3S+ are in excellent agreement with experimental values and that the addition of water to all three ions is energetically more favorable than solvation by H2S. As clusters grow in size, the energetic trends of cluster hydration begin to reflect those for bulk H2O liquids, i.e. calculated hydration enthalpies and entropies approach values characteristic of the condensation of bulk water (ΔHo = -44.0 kJ mol-1, ΔSo = -118.8 J K mol-1). Water and hydrogen sulfide cluster calculations at higher temperatures indicate that a significant fraction of H3O+, NH4 + and H3S+ ions exists as solvated moieties. © 2008 Elsevier Ltd. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/72614
ISSN
2015 Impact Factor: 4.315
2015 SCImago Journal Rankings: 3.016
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorLemke, KHen_HK
dc.contributor.authorSeward, TMen_HK
dc.date.accessioned2010-09-06T06:43:29Z-
dc.date.available2010-09-06T06:43:29Z-
dc.date.issued2008en_HK
dc.identifier.citationGeochimica Et Cosmochimica Acta, 2008, v. 72 n. 14, p. 3293-3310en_HK
dc.identifier.issn0016-7037en_HK
dc.identifier.urihttp://hdl.handle.net/10722/72614-
dc.description.abstractReports of the high ion content of steam and low-density supercritical fluids date back to the work of Carlon [Carlon H. R. (1980) Ion content of air humidified by boiling water.J. Appl.Phys.51, 171-173], who invoked ion and neutral-water clustering as mechanism to explain why ions partition into the low-density aqueous phase. Mass spectrometric, vibrational spectroscopic measurements and quantum chemical calculations have refined this concept by proposing strongly bound ion-solvent aggregates and water clusters such as Eigen- and Zundel-type proton clusters H3O+·(H2O)m and the more weakly bound water oligomers (H2O)m. The extent to which these clusters affect fluid chemistry is determined by their abundance, however, little is known regarding the stability of such moieties in natural low-density high-temperature fluids. Here we report results from quantum chemical calculations using chemical-accuracy multi-level G3 (Curtiss-Pople) and CBS-Q theory (Peterson) to address this question. In particular, we have investigated the cluster structures and clustering equilibria for the ions H3 O+ · (H2 O)m (H2 S)n, NH4 + · (H2 O)m (H2 S)n and H3S+·(H2O)m(H2S)n, where m ≤ 6 and n ≤ 4, at 300-1000 K and 1 bar as well as under vapor-liquid equilibrium conditions between 300 and 646 K. We find that incremental hydration enthalpies and entropies derived from van't Hoff analyses for the attachment of H2O and H2S onto H3O+, NH4 + and H3S+ are in excellent agreement with experimental values and that the addition of water to all three ions is energetically more favorable than solvation by H2S. As clusters grow in size, the energetic trends of cluster hydration begin to reflect those for bulk H2O liquids, i.e. calculated hydration enthalpies and entropies approach values characteristic of the condensation of bulk water (ΔHo = -44.0 kJ mol-1, ΔSo = -118.8 J K mol-1). Water and hydrogen sulfide cluster calculations at higher temperatures indicate that a significant fraction of H3O+, NH4 + and H3S+ ions exists as solvated moieties. © 2008 Elsevier Ltd. All rights reserved.en_HK
dc.languageengen_HK
dc.publisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/gcaen_HK
dc.relation.ispartofGeochimica et Cosmochimica Actaen_HK
dc.subjectAggregate-
dc.subjectAqueous solution-
dc.subjectEquilibrium-
dc.subjectIon-
dc.subjectMass spectrometry-
dc.titleSolvation processes in steam: Ab initio calculations of ion-solvent structures and clustering equilibriaen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0016-7037&volume=72&issue=14&spage=3293–3310&epage=&date=2008&atitle=Solvation+processes+in+steam:+Ab+initio+calculations+of+ion-solvent+structures+and+clustering+equilibriaen_HK
dc.identifier.emailLemke, KH:kono@hkucc.hku.hken_HK
dc.identifier.authorityLemke, KH=rp00729en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1016/j.gca.2008.02.024en_HK
dc.identifier.scopuseid_2-s2.0-45849152650en_HK
dc.identifier.hkuros153261en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-45849152650&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume72en_HK
dc.identifier.issue14en_HK
dc.identifier.spage3293en_HK
dc.identifier.epage3310en_HK
dc.identifier.eissn1872-9533-
dc.identifier.isiWOS:000257697300001-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridLemke, KH=24168776600en_HK
dc.identifier.scopusauthoridSeward, TM=35332875900en_HK

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