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Aggregation-induced dissociation of HCl(H2O)4 below 1 K: the smallest droplet of acid

Gutberlet, Anna and Schwaab, Gerhard and Birer, Özgür and Masia, Marco and Kaczmarek, Anna and Forbert, Harald and Havenith, Martina and Marx, Dominik (2009) Aggregation-induced dissociation of HCl(H2O)4 below 1 K: the smallest droplet of acid. Science, Vol. 324 (5934), p. 1545-1548. eISSN 1095-9203. Article.

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DOI: 10.1126/science.1171753

Abstract

Acid dissociation and the subsequent solvation of the charged fragments at ultracold temperatures in nanoenvironments, as distinct from ambient bulk water, are relevant to atmospheric and interstellar chemistry but remain poorly understood. Here we report the experimental observation of a nanoscopic aqueous droplet of acid formed within a superfluid helium cluster at 0.37 kelvin. High-resolution mass-selective infrared laser spectroscopy reveals that successive aggregation of the acid HCl with water molecules, HCl(H2O)n, readily results in the formation of hydronium at n = 4. Accompanying ab initio simulations show that undissociated clusters assemble by stepwise water molecule addition in electrostatic steering arrangements up to n = 3. Adding a fourth water molecule to the ringlike undissociated HCl(H2O)3 then spontaneously yields the compact dissociated H3O+(H2O)3Cl ion pair. This aggregation mechanism bypasses deep local energy minima on the n = 4 potential energy surface and offers a general paradigm for reactivity at ultracold temperatures.

Item Type:Article
ID Code:2773
Status:Published
Refereed:Yes
Uncontrolled Keywords:Acid dissociation, acid HCI
Subjects:Area 03 - Scienze chimiche > CHIM/02 Chimica fisica
Divisions:002 Altri enti e centri di ricerca del Nord Sardegna > INSTM-Consorzio Interuniversitario Nazionale per la Scienza e la Tecnologia dei Materiali, Unità di ricerca di Sassari
001 Università di Sassari > 01 Dipartimenti > Chimica
Publisher:American Association for the Advancement of Science
eISSN:1095-9203
Deposited On:20 Aug 2009 09:54

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