Publication: Aggregation-induced dissociation of HCl(H 2O) 4 below 1 K: The smallest droplet of acid
Program
KU-Authors
KU Authors
Co-Authors
Advisor
Publication Date
2009
Language
English
Type
Journal Article
Journal Title
Journal ISSN
Volume Title
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(H 2O) 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(H 2O) 3 then spontaneously yields the compact dissociated H 3O +(H 2O) 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.
Description
Source:
Science
Publisher:
American Association for the Advancement of Science
Keywords:
Subject
Chemistry