Hamburg 2009 – wissenschaftliches Programm

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SYHR: High resolution spectroscopy – modern trends and new techniques

SYHR 1: High resolution spectroscopy - modern trends and new techniques I

SYHR 1.2: Hauptvortrag

Donnerstag, 5. März 2009, 11:10–11:50, VMP 8 R05

Some like it cold – aggregation and dissociation of HCl and water in helium nanodroplets — Gerhard Schwaab¹, •Ozgur Birer², Anna Gutberleth¹, and Martina Havenith¹ — ¹Physical Chemistry II, Ruhr University Bochum, D-44780 Bochum, Germany — ²Chemistry Department, Koc University, Rumelifeneri Yolu, Sariyer 34450 Istanbul, Turkey

Helium nanodroplets provide a gentle, ultracold matrix for studies of agglomeration processes. Due to the superfluidity of He at 0.37 K a combination with high-resolution infrared spectroscopy provides an ideal tool to separate local and global minimum structures of aggregates.

We used Helium nanodroplets in combination with a cw OPO and a mass spectrometer as detector unit to study the aggregation and solvation of HCl in water. Besides signals of pure HCl, undissociated HCl-H₂O, and rotationally resolved HCl dimer, broadened peaks around 2670 cm⁻¹ were found. Optically selective mass spectroscopy (OSMS) allowed unambiguous assignment of the according parent species as solvent separated ion pair H₃O⁺(H₂O)₃Cl⁻. A replacement of HCl by DCl produced a slight spectral shift and a further splitting. This is in excellent agreement with theoretical calculations.

The observation of, what we believe is the ”smallest droplet of an acid”, opens the way for spectroscopic investigation of microsolvation processes at ultracold temperatures such as zwitterion formation of amino acids.