EGAS41 - Swansea University

41 st EGAS PL 7 Gdańsk 2009
Chemistry at ultracold temperatures:
Observation of the smallest droplet of acid
Martina Havenith
Physical Chemistry II, NC 7/72, Ruhr University Bochum, 44780 Bochum, Germany
E-mail: martina.havenith@rub.de
Acid dissociation and subsequent solvation of its charged fragments, including the hydrated
proton, is one of the most fundamental chemical processes. In contrast to ambient
bulk water environments, understanding mechanisms that allow for ionization in small
networks at ultracold conditions are relevant from atmospheric to interstellar chemistry,
but remain largely unexplored.
In Bochum we have set up a He-nanodroplet apparatus in combination with a homebuilt
cw-Optical Parametric Oscillator IR (OPO) with full frequency coverage in the
range from 2600 to 3400 cm −1 , high output power (up to 2.7 W), and high resolution
(0.0001 cm −1 ) [1]. Briefly (35), helium droplets with an average size of 8500 He were
formed in a supersonic expansion of precooled (16 K) gaseous helium through a 5 µm
diameter nozzle. These droplets provide a gentle matrix for step-by-step aggregation of
molecular clusters, via a controllable pickup process governed by Poisson’s statistics [2],
allowing for IR high-resolution spectroscopy.
We report the first experimental observation of a microscopic aqueous droplet of acid
reported at ultracold (0.37 K) temperatures. Furthermore we will discuss specific reaction
mechanism at ultracold temperatures [3]. Here, we report full dissociation of a single HCl
molecule with exactly four water molecules in superfluid helium nanodroplets as a result
of molecular aggregation at 0.37 K.
References
[1] K. von Haeften, A. Metzelthin, S. Rudolph, V. Staemmler, M. Havenith, Phys. Rev.
Lett. 95, 215301 (2005)
[2] J.P. Toennies, A.F. Vilesov, Angew. Chem. Int. Ed. 43, 2622 (2004)
[3] A. Gutberlet, G. Schwaab, Ö. Birer, M. Masia, A. Kaczmarek, H. Forbert, M. Havenith,
D. Marx, Science, in press
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